I had the same issue. What I did.
Created new admin account using System Preferences.
Logged out of current account
Connected using screen sharing with new admin name and pass.
Logged in to machine as "old" user
Screen sharing with "old" user works now
i had this issue too i use TightVNC on Win7 at work. it was intermittant and slow at best compared to Snow Leopard. I found settings under tight VNC that work well. and MochaVNC for iP/ad/hone/od just got updated and supports Lion now
Tight VNC the most important one that affect perfomrance is Encoding I found Zlib(pure) is the best setting i also have compression set to fast and alllow jpg comporession set to quality 6
its better now still not as silky smooth as Snow Leopard was
This is what has worked for me:
1. Decrease the screen resolution to the lowest possible setting
2. Connect via a VNC client
3. Once past the login screen, restore the screen resolution to your heart's desire
If it still freezes for you, try entering your password quickly in the login screen.
Before you disconnect, you may want to decrease the resolution again for the next time (in case you won't have physical access to your mac).
I'm on 10.7.1, and even afer a reinstall of Lion, it's still locking up. I'd try the suggestions given above regarding desktop sharing settings, but now the sharing preferences pane locks up System Preferences. >_<
Solution for Chicken of the VNC -- Click the Allow Other Clients to Connect checkbox. This will enable the login screen and allow you to type your password. Not optimal, I would prefer to auto-connect but it works.
Sadly, of course, none of these methods has fixed the underlying problem - VNC clients can't connect to 10.7 from Windows.
You can do anything you like with colours, new admin accounts, upgrading to 10.7.4, trying not having the machine logon, it doesn't matter. Apple broke the server at the backend and it won't be stable for you.
We've got a bucketload of mac minis here with a raft of client machines on windows and, on 10.6.8, all windows clients can connect to all clients.
Once you put one on Lion, bang, grey screens and you can use what ever client you like.
The waters have been muddied by suggestions of fixes and people who don't understand it's not apple to apple that's broken (Chicken of the vnc etc), but at the end of the day, my department still can't move to 10.7 as of July 2012.
1) Turn on screen sharing on the mac running 10.7
2) Load up Real VNC Viewer on your PC
3) Set password on the MAC under screen sharing settings to allow VNC connections.
4) VNC to the MAC using the password.
5) You should see the grey fabric screen
6) Type your username then press enter
7) Type your passowrd then press enter
NOTE: you will not see anything text on the screen.
8) You should now see your screen