I just discovered an odd bug (or unwanted interaction) with the XP tools mouse driver. If a key is pressed when the mouse exits the window, then the key appears to the VM to remain pressed when the mouse returns to the window - even if it has subsequently been released. I noticed this with the command key, which causes all manner of odd things to occur when you move back into the window and start typing, as Windows then interprets the keys as being start menu shortcuts. However, you can repeat the effect with any key. Admittedly you might not normally hit this problem, but if you hit command-H to hide Parallels, then when you return to it again, the command key will appear to still be depressed. When using it fullscreen, command-H seems a pretty sensible thing to want to do to use other apps.
So now that you've cracked the fullscreen sizing on my MacBook, I'm using Parallels much more seriously. With Virtue (much thanks to the person who pointed me at that on this forum) I can run Parallels fullscreen and flick between it and my other apps with keyboard shortcuts. However, this means I now frequently leave the Parallels window with modifier keys held down so this has become much more of a pain as I have to flick the keys when I come back to make Parallels realise they've been released. If you guys can figure out a solution to this I'll be a very happy man. Based on the progress this app is making I will definitely be purchasing it.