First the bad news, VB doesn't support enough 3d features to run Aero (neither does VMware). I did discover a work around though, connect to your virtual machine using Remote Desktop Connection from a Vista machine, turn all graphics options to high and volia.
While I had VB installed, I did a quick and dirty comparision with VMware workstation using Windows Performance Index. Take these results with a grain of salt, I didn't spend much time playing with the setup and tweaking. I couldn't get dual core to work on VB, it just blue-screened, and I didn't have the time to spend sorting it out.
Windows Performance Index
|Virtual Box |
|Primary Hard disk||5.4||5.3||5.4||4.7|
The memory figures are surprising, I am not sure if the VB figures of 5.9 are real or just a sign of something wrong somewhere. Draw your own conclusions on that.
VB is slower in hard drive, but otherwise up with the play processor wise. Getting dual core working would probably give similar processor figures to VMware dual core.
I was impressed with how well VMware matches up to the host system. While VB doesn't seem to be quite there yet, it is still doing pretty well, and you can't beat the price.