We use UltraVNC to connect to our customers but we've been having problems since Windows started going to 64 bit. It ran so slowly it made it difficult to use. The refresh rate was horrendous. At first we thought it was because of the Windows Aero scheme, but even when we turned it off it still didn't act right.
I found out if you completely uninstall the product, reboot, and reinstall without checking the box to install as a service it works like it did in 32 bit. Pretty weird!
So all of us uninstalled and made the change and now the program works great again.