After booting a windows 2003 guest, I can copy/paste from the host clipboard without problem. If I suspend the guest and then resume it I can't copy/paste to or from the host anymore. I have to reboot the guest for the clipboard to work.
I've experienced this as well. My work-around (rather than restarting Windows) is to go run the Parallels Tools Center (C:\Program Files\Parallels\Parallels Tools\ParallelsToolsCenter.exe) and Disable then Enable Clipboard Synchronizing. This really should be addressed by the Parallels folks since clipboard sharing is one of the most useful features of Desktop for Mac. Mark