QueryFrame very slow on Windows
I had same issue and I found out that this is caused by prolonged exposure. It may be the case that Windows drivers increased exposure to increase brightness of picture. Try to point your camera to light source or manually set decreased exposure
I have build a simple webcam recorder on linux which works quite well.
I get ~25fps video and good audio.
I am porting the recorder on windows (win7) and while it works, it is unusable.
The QueryFrame function takes something more than 350ms, i.e 2.5fps. 
The code is in python but the problem really seems to be the lib call.
I tested on the same machine with the same webcam (a logitech E2500). 
On windows, I installed openCV v2.2. I cannot check right now but the version might be a bit higher on Ubuntu. 
Any idea what could be the problem ? 
edit : I've just installed openCV2.4 and I have the same slow speed.