Screen Sharing stopped working after Lion upgrade
Not at all - I have three classes of macs that all worked flawlessly with the upgrade to Lion. They all share their screens with the basic VNC technology:


basic OS X - turn on VNC or remote management - bonjour location is local
basic plus MobileMe back to my mac for locating the mac over the internet
basic plus Screens app from edovia to locate the mac over the internet


I haven't seen a good Apple writeup of the Lion changes - but when you log in with your OS account rather than with the VNC password - you get a distinct loginwindow process for that account whether or not that user is shown as logged in locally. This change could be causing you grief.

Put another way - screen sharing and log in is now a virtual concept - you are no longer limited to one mac log in session or tied tightly to the physical screen. User A can be using the mac and User B logs in remotely and gets their own workspace rather than seeing what A is doing or forcing A to log off.

The writeup inside the screens app is nice if you have purchased it.