I recently upgraded to Vista Ultimate and I found that my Messenger Live Beta 8.1 keeps crashing. I guess this is not an issue for everyone, but it is for me. I Googled the problem and found a great post by Mary Jo Foley http://blogs.zdnet.com/microsoft/?p=103
This is the fix that Mary Jo put out there from MS. Read her post for all the details.
The Microsoft-suggested workaround:
1. Uninstall Flash Player (Click Start->Control Panel->Uninstall a Program, then select Flash Player)
2. Close Windows Live Messenger and any other programs that use Flash
3. Open Adobe public Flash Player beta site (http://labs.adobe.com/downloads/flashplayer9.html)
4. Click "Download Installer for Windows Active X" to install
It seems that Messenger is working much better and that I can actually use my sharing folders now (w00t !). Just wish they could play together nicely right out of the box.
Hope this helps
-paul