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.