Actually Lion brought a lot of changes to the Mac - whether you'll find them useful is another question. With 10.7 Apple began making the Mac OS look more like iOS which some people liked and others didn't. For those of us who use an iPhone, iPad, or iPod, having the AddressBook, Mail, and Calendar behave similarly on both platforms was nice. FileVault now encrypts the entire hard drive rather than just the user's directory. Push notifications came to the Mac. Multi-touch is much more useful on Macs with trackpads. Fullscreen mode for Apps is very useful for small screen Macs.
The last 'feature' may be less useful. Apple dropped support for Rosetta so if you haven't been keeping your software up to date and have some software from the PPC days, they will no longer function.
Apple dropped support for Rosetta so if you haven't been keeping your software up to date and have some software from the PPC days, they will no longer function.
Not entirely accurate, so as to potentially mislead the OP to think that he does not have options...
To the OP: if you are running Snow Leopard and have software that is 6+ years old, you are most likely running what is known as PowerPC software, which requires Rosetta to run and as dwp accurately suggests is missing from Lion and Mountain Lion.
However their are four generally accepted workarounds to dealing with this problem; all of which should work with your computer:
1. Stay with Snow Leopard;
2. Partition your hard drive or add an external one and install Snow Leopard (with the optional Rosetta) and have the ability to "dual-boot" into Snow Leopard to run your PowerPC applications, and into Lion or Mountain Lion with iCloud, as needed;
3. Update your PowerPC software to Intel compatible versions, if such upgrades exist, and/or find alternative software that will open your data files, modify them as needed and then save these changes; if such alternatives exist; and
4. Install Snow Leopard (with Rosetta) into Parallels and have the ability to concurrently run your PowerPC applications with Lion or Mountain Lion:
[click on image to enlarge]
NOTE: Computer games with complex, 3D or fast motion graphics make not work well or at all in virtualization.
In the Apple Menu, if you do an About this Mac and then More Info, under Software, look for what applications are listed as PowerPC. Let us know which of these are important to your use on an ongoing basis and we can respond to you in more precise detail.