I'm trying to enable/use 3D acceleration in a Ubuntu guest running in VirtualBox with Guest Additions on a Windows host. Although I think the 3D acceleration is being enabled, the performance of my guest takes a nosedive; the machine almost comes to a crawl.

Is this a known issue? Is there a known fix/workaround?
How can I verify the status of 3D acceleration in my Ubuntu guest? What commands to run? What log files can I look at?

My setup ...

ATI Radeon 6770M graphics card (2GB)
Windows 7 Home Premium (64-bit)
VBox 4.1.6 (with Guest Additions)
Ubuntu 11.10 (32-bit) (The problem exists on 64-bit Ubuntu as well.)