On the Rebel XTi, I get 25-30 images at three frames/second. And once the buffer fills up, the camera is done until it finishes writing everything out. On my Canon 40D, it does 6.5 frames/second ... which while quieter than the XTi (even more so in real life than the video suggests) it sounds like a machine gun! As shown, I was able to shoot 50 frames at large JPEG ... but this was at ISO3200 ... it turns out the burst depth is highly dependant on ISO, and I was able to shoot 89 frames with ISO100 - WOW!
After that, it then drops to about one/frame second - i.e. the camera keeps shooting as it writes out data to the card. Note that high ISO noise reduction - CFII.2 - is turned OFF - if this is turned on, the 40D shows I only have six shots and with writing to the CF card, I was only able to get 7 shots off before the 40D slows down ... in ISO100 or ISO3200. Note that even if you show RAW, you still get those 7 shots ... so this implies that the camera is CPU limited by processing the noise reduction algorithms.
If you want to see the 6.5 fps in action, check out the
Canon 40D autofocus page.
The Canon 40D high ISO shootout may also be of interest - CFII.2 makes a difference.
BTW, the Canon 40D shows the burst depth in the viewfinder window before
you even get started. Presumably, this is how much the in-camera buffer
can store before it has to write to the memory card. The faster the
memory card, the more frames above that number
you'll be able to fire. Specifically, the Canon 40D displays the number
of shots available as 75 (ISO100), 74(200), 63(400), 60(800), 57(1600),
and 49(3200). Page 57 of the manual says that burst depth varies with
"subject, CF card brand, ISO Speed, Picture Style, etc" ... but I
didn't think it would be that significant. Note that I was actually
able to get 89 frames at ISO100 before the Canon 40D slowed down
shooting the same scene.
By then, you should have been able to get the shot! ;-)
While the above shots where with a SanDisk 2 GByte Ultra II CF card,
I upgraded a while later, and here's some tests with the
Sandisk Extreme III 8 GByte on the 40D.
P.S. A few years later, Buzz helped me test a Canon 70-200 2.8 IS II lens with 2x TC's!