A Basic Guide for Data Migration
If you are migrating a PowerPC (PowerMac) system (G3, G4, or G5) to an Intel-Mac be careful what you migrate. Keep in mind that some items that may get transferred will not work on Intel machines and may end up causing your computer's operating system to malfunction.
Note: if you are upgrading to a Mac with Mac OS X 10.7 (Lion) or later, or with the intent of upgrading to 10.7 or later anytime in the future, be aware that any applications that are not labelled Universal, or haven't been upgraded to Intel CPU compatibility will not run on Lion or later. Documents may migrate if an Intel native application exists that will open them, but applications that are PowerPC only will not. This user tip explains what else is needed for upgrading to Lion: https://discussions.apple.com/docs/DOC-2465.
This also means for any Mac model whose hardware or firmware that has been refreshed on or after July 20, 2011, you won't be able to install 10.6.8 or get Rosetta from it unless you follow a link at the end of this tip. It may be better to get a used or refurbished Mac that predates July 20, 2011. See the Snow Leopard tip on the bottom for which Macs support Rosetta, which in turn supports older PowerPC applications.
Both Leopard (10.5) , and Tiger (10.4.4 through 10.4.11, excluding 10.4.0, 10.4.1, 10.4.2, and 10.4.3) have PowerPC and Intel Mac support, and upgrading to either, this tip here, as well as links to my tip on Tiger and Leopard will help with your upgrade.
The Knowledgebase article Intel-based Mac: Some migrated applications may need to be updated refers to methods of dealing with migrating from PowerPC chips to Intel with the Migration Assistant safely. The authors of this tip have not had a chance to verify this works in all instances, or that it avoids the 10.6.1 and earlier Guest Account bug that caused account information to get deleted upon use of the Migration/Setup Assistant. However, a well backed up source that includes at least two backups of all the data that are not connected to your machine will help you avoid potential issues, should they arise. In event it does not work, follow the steps below.
Rosetta supports "software that runs on the PowerPC G3, G4, or G5 processor that are built for Mac OS X". This excludes the items that are not universal binaries or simply will not work in Rosetta:
Classic Environment, and subsequently any Mac OS 9 or earlier applications
Screensavers written for the PowerPC
System Preference add-ons
All Unsanity Haxies
Browser and other plug-ins
Contextual Menu Items
Applications which specifically require the PowerPC G5
Java applications with JNI (PowerPC) libraries
See also What Can Be Translated by Rosetta.
In addition to the above you could also have problems with migrated cache files and/or cache files containing code that is incompatible.
If you migrate a user folder that contains any of these items, you may find that your Intel-Mac is malfunctioning. It would be wise to take care when migrating your systems from a PowerPC platform to an Intel-Mac platform to assure that you do not migrate these incompatible items.
If you have problems with applications not working, then completely uninstall said application and reinstall it from scratch. Take great care with Java applications and Java-based Peer-to-Peer applications. Many Java apps will not work on Intel-Macs as they are currently compiled. As of this time Limewire, Cabos, and Acquisition are available as universal binaries. Do not install browser plug-ins such as Flash or Shockwave from downloaded installers unless they are universal binaries. The version of OS X installed on your Intel-Mac comes with special compatible versions of Flash and Shockwave plug-ins for use with your browser.
The same problem will exist for any hardware drivers such as mouse software unless the drivers have been compiled as universal binaries. For third-party mice the current choices are USB Overdrive or SteerMouse. Contact the developer or manufacturer of your third-party mouse software to find out when a universal binary version will be available.
Also be careful with some backup utilities and third-party disk repair utilities. Disk Warrior 4.1, TechTool Pro 4.6.1, SuperDuper 2.5, and Drive Genius 2.0.2 work properly on Intel-Macs with Leopard. The same caution may apply to the many "maintenance" utilities that have not yet been converted to universal binaries. Leopard Cache Cleaner, Onyx, TinkerTool System, and Cocktail are now compatible with Leopard.
Before migrating or installing software on your Intel-Mac check MacFixit's Rosetta Compatibility Index.
Additional links that will be helpful to new Intel-Mac users:
Because Migration Assistant isn't the ideal way to migrate from PowerPC to Intel Macs, using Target Disk Mode, copying the critical contents to CD and DVD, an external hard drive, or networking will work better when moving from PowerPC to Intel Macs. The initial section below discusses Target Disk Mode. It is then followed by a section which discusses networking with Macs that lack Firewire. You can also determine if you have Firewire by looking at this image of the ports typically found on a PowerMac G4 Firewire 800, which has two 6 pin Firewire 400 (IEEE 1394a) ports below the USB ports, and below that, a Firewire 800 (IEEE 1394b).
The 4 pin Firewire found on many camcorders is just a Firewire 400 port that is not powered by the computer. Cables exist that can convert between all three.
If both computers support the use of Firewire then you can use the following instructions:
1. Repair the hard drive and permissions using Disk Utility.
2. Backup your data. This is vitally important in case you make a mistake or there's some other problem.
3. Connect a Firewire cable between your old Mac and your new Intel Mac.
4. Startup your old Mac in Target Disk Mode.
5. Startup your new Mac for the first time, go through the setup and registration screens, but do NOT
migrate data over. Get to your desktop on the new Mac without migrating any new data over.
If you are not able to use a Firewire connection (for example you have a Late 2008 MacBook that only supports USB:)
1. Set up a local home network: Creating a small Ethernet Network.
2. If you have a MacBook Air or Late 2008 MacBook see the following:
Copy the following items from your old Mac to the new Mac:
In your /Home/ folder: Documents, Movies, Music, Pictures, and Sites folders.
In your /Home/Library/ folder:
/Home/Library/Application Support/AddressBook (copy the whole folder)
/Home/Library/Application Support/iCal (copy the whole folder)
Also in /Home/Library/Application Support (copy whatever else you need including folders for any third-party applications)
/Home/Library/Keychains (copy the whole folder)
/Home/Library/Mail (copy the whole folder)
/Home/Library/Preferences/ (copy the whole folder)
/Home/Library/Calendars (copy the whole folder)
/Home/Library/iTunes (copy the whole folder)
/Home/Library/Safari (copy the whole folder)
/Home/Library/Syndication (Tiger) or /Home/Library/PubSub (Leopard) <<< RSS
Credit goes to iBod for this information.
If you want cookies:
For Entourage users:
Entourage is in /Home/Documents/Microsoft User Data
Also in /Home/Library/Preferences/Microsoft
Credit goes to Macjack for this information.
If you need to transfer data for other applications please ask the vendor or ask in the Discussions where specific applications store their data.
5. Once you have transferred what you need restart the new Mac and test to make sure the contents are there for each of the applications.
Special instructions for those who have purchased Mac models that do not support Rosetta:
The newest (post 2010) Mac models run only Lion or Mountain Lion. They are not able to run Snow Leopard at all. However, you can still run PPC applications using Snow Leopard and Rosetta by intalling Snow Leopard as a virtual machine using Parallels. This is not an exercise for the truly inexperienced user, but it is completely doable provided you are willing to spend some money and some time. For complete instructions on what to do see https://discussions.apple.com/message/18280105#18280105. Although the instructions are keyed to Parallels 7, you should instead use the latest version, Parallels 8. (This information was contributed by user MlchaelLAX.)