two days ago I have discovered a memory leak in VB 3.0.12 which I describe here.
Since there has been no response to my post, I tried to install 3.1 beta2 to see if the problem is present here too. After uninstalling 3.0.12 GA and installing 3.1b2 GA, I got the same error.
To reproduce the problem:
Vista 32bit host, XP SP3 32bit guest, VB 3.1 beta2
install GA in safe mode
install MS Visual Studio 2010 Ultimate beta from .iso file (I have not tried the web installer.)
enable 3D acceleration (2D acceleration grayed out in my case)
run MS VS 2010, wait for the main window to appear, watch memory usage of the VirtualBox.exe process
Log is attached, I had to divide it because of attachment size limitations.