Sometimes the guest simply freezes up, with the screen displaying garbled graphics (black background with multi coloured dots). When I reset the guest, it will boot then hang on a BSOD. I've tried nearly every combination of settings for the guest machine (enabling 3d acceleration, video memory size), but this still occurs randomly, and doesn't seem to be connected with any particular action I take. The only way to get the guest running again is to turn it off, then turn it back on again. If anyone has any clue as to what could cause a problem like this I'd be most appreciative to hear it.
I thought I'd post here before opening a ticket on the public bugtracker. Let me know if you would like any log files or more information. Thanks.
(There is another issue with the Windows 7 guest that I managed to sort of get around. The audio used to skip quite a lot when using Winamp or other audio applications, but I found if you have another guest VM open along with the Windows 7 guest, it stops that happening. I made a blank guest especially for this, and as long as it's open in the background, Windows 7 audio is butter smooth and silky lovely. It's very wierd...)
EDIT: Added screenshot showing corrupt graphics in Windows 7 guest.
Graphical corruption in VirtualBox 3.0.4 when running Windows 7 Home Premium as guest.