Just an FYI: if you haven't installed Apple's security update 2007-009, don't install it unless you want to lose your cut-n-paste functionality (otherwise known as the clipboard synchronization in the Parallels Tools Center) as well as some drag-n-drop features between OS' as well. To be more specific, you can copy text from the Parallels Guest VM to the Mac OSX, but not from Mac OSX to the Guest VM (people have reported the same problem on both Leopard and Tiger. It seems that the CoreFoundation.framework was modified with the above update and broke other Mac OSX features as well.
Evidently, the Parallels team is working hard on a update that is due out in January to fix this. In the meantime, the issue is being discussed in both the Parallels Forums and in the Apple Forums. (I am subscribed to the Parallels thread, so I'll post an update as soon as I hear anything).
Update (01/09/08): Evidently, the Parallels team has fixed this issue in-house and are in the process of QA'ing it now. ....Waiting patiently....
Update (01/18/08): At last, a Parallels update is available for this issue (build# 5584). Several users have reported back on the forum thread that this appears to take care of the very annoying cut-n-paste problem. I have installed the update and am pleased to say that I have my cut-n-paste back between Parallels and Mac OSX apps. Yes!