I have been getting quite a few questions on OSX Lion, most of the interest is in the iCloud feature.
I'll include links below to replacement products, more information, or potential workarounds. If you have more information, please sign in (link at bottom of screen) and leave a comment.
One of the biggest issues is support has been removed for Rosetta, which allows Macs to use older PowerPC applications. PowerPC binaries no longer run in Lion.
Lion also reversed the way scrolling works on the touchpad to be more similar to IOS devices or a physical desktop, problem is they said they've been doing it wrong for almost 30 years, that's a bit of muscle memory.
If you still hate it
Another issue is that Lion no longer ships with Java so you may need to download it. You can download it through software update (some apps prompt you to when you try to open them) or the java.com webpage. Apps with potential Java issues:
You can look up support for your application at http://roaringapps.com/apps:table
Some applications that no longer function or have significant issues.
Many apps including Adobe Creative Suite and Microsoft Office 2011 have limited support for Lion feature such as Auto-Save, full screen apps, and restoring state after restart.
Useful Links: mostly for Systems Administrators