Some questions have been posed as to Lion's upgrade. As end users experienced in past upgrades, we can tell you the following truths that should hold based on announcements in http://www.apple.com/pr/ and http://www.apple.com/macosx/
Q: What are the system requirements of the Lion upgrade?
A: Core2Duo, Core i3, i5, i7, and Xeon Intel CPUs with 2 GB of RAM in a Macintosh computer with 2 GB of RAM, and 4 GB for downloading from the Mac App Store (Available in 10.6.6 and later). Unofficially, past upgrades have arbitrarily also required an additional 15% of the hard drive to be free for data.
Q: Are there any pitfalls to watch out for?
A: With all upgrades, backing up your data at least twice has been a given. Hardware can fail independently of downloads and upgrades, though may happen simultaneously. Software may be found to be incompatible that has not been tested with the new upgrade, or combination of other software that might be installed with the upgrade. It is also strongly recommended once your backup is complete, to shut down your computer, remove all but Apple wired keyboard and mouse (notebooks remove all input devices). Then once done, reboot, and go directly to the upgrade distribution system available.
Third party system tools, modification, and "maintenance" applications should be verified as compatible, or removed until known to be compatible. Check with developers how to remove if it is essential to use Lion before those applications become compatible. Most "maintenance" tools that deal with system cache, prebinding, are not really maintenance tools. Ask on forum when are the appropriate times to use them before assuming they should be used for upgrades or otherwise.
Q: How can I get from 10.4 or 10.5 to 10.6.6?
A: Purchase a 10.6 retail installer from an Apple retail or third party reseller. It has a picture of a Snow Leopard on the DVD, and does not say Upgrade, Dropin, or OEM. Install it, and then install the 10.6.6 combo update from:
Q: Is it true that I can only get it from the Mac App Store?
A: Presently this truth is based on current documentation as of the writing of this article. It may change, but we can't speculate as to its change. It has a better chance of changing if users request something different at:
Q: What limitations might one encounter if it doesn't change?
A: A 5 Mbps internet connection can download Lion in 2 hours. A 768Kbps connection can download it in 13 hours. These times do not including installation time, or variabilities in connection speeds from a non-dedicated connection, or background application usage of the internet. Any applications running when the installation process begins might interfere with the installation itself, and they should be quit first. It is unknown at the present time if each individual computer will have to download it separately on the same connected Local Area Network, or if imaging of the downloaded file will be allowed for distribution on certain sized Local Area networks in certain settings (schools, businesses, and homes). This is a question one should post or look for on Apple Support Communities once Lion becomes available through regular channels, to determine if there are any limitations.
Q: When will Lion become available?
A: Sometime in July 2011 according to present forecasts from Apple on their own website.
Q: Are any applications known not to be compatible with Lion?
A: Not until the release date.