Technically, the burst rate (speed) is the number of images the camera can take before the buffer fills up:
In practice, the term is used to refer to the number of shots per second the camera can record:
DPR's review of the G12 puts it at 2 per second:
On the G12, you enable "continuous shooting" on the Function menu, then fire away!
Practically speaking, the G12 (or other compacts) are not the right tool for action photography, where you may need to fire off 4-5 shots/second.
"Careful photographers run their own tests." - Fred Picker