Unfortunately Parallels have lost me as a customer. I started with PD3 and found that my Mac would Kernel Panic if PD3 and EyeTV was open at the same time (which was often the case). Got told that for the fix, I would have to pay and update to PD4 which I did.
PD4 ran OK, but I could never get the Parallels tools to install, which made things very tedious. I could not copy and paste between Mac and Windows and could only get the mouse cursor to work if I Option + Cmd'ed the PD4 window each time. Again I got told that this was a known issue relating to my Mac model, and the bug fix was only available through PD5.
I got PD5 via the MacUpdate Promo bundle. But for whatever reason I found this version very sluggish. Again Parallels admitted there were problems but could not say when it would be fixed. Just kept getting canned responses, words to the effect "our engineers are aware of this issue and are working towards a fix".
So I changed to VirtualBox instead at that point, at the start of this year. Have found VirtualBox to be a brilliant solution. It starts and saves Windows 7 virtual machines in under 10 seconds and the performance and stability is simply outstanding. I've never once had VirtualBox crash on me and it survived the transition to Lion without requiring any updates. Like others have commented, if VirtualBox was paid software, I'd happily spend the money on it. The fact that it is free software is brilliant and I have no intentions of going back to Parallels ever again. Just my 2 pence worth.