I use UltraVNC 126.96.36.199, and I am having some trouble when using Excel 2007 remotely. The main issue is that the viewer seems to hang when I copy a large number of cells (thousands). As soon as I have given the copy command through the right-click menu or the main menu, the screen stops updating. Looking at the status window, the server seems to be sending data to my viewer. It also seems that the server is still registering mouse movements and clicks, because after closing the viewer and opening a new one the selections I previously tried to make on the hanged screen are active.
I have disabled clipboard transfer, which used to cause me problems as well (copying a large area would simply take down the connection as it was flooded with clipboard info), so I know it's not that.
Another problem I have with Excel and UltraVNC is that typing numbers into cells will occasionally cause a new workbook to appear, as if I had held down Alt or Ctrl or something while typing.
Both problems mainly appear over a slow connection.