i worked on a macbook pro (older version) last night that was having parallels problems - we uninstalled and reinstalled XP, as described in other threads. Seems to be running fine now. But he siad it wokred great for about two weeks before he had problems. my suggestion was to make sure Windows Update is ON and automatically installing new software updates.
I use bootcamp on my new MP - not really interested in the hot switch - but then i have taken the time and $ to duplicate my software on both platforms where ever i can so i dont need the hot switch.
I would fault windows before blaming parallels, but whats new.