Recently my 30D started to go Err99 and sound like it was flipping the mirror sporadically. This was on top of focusing and shutter button problems I was having. Happened with multiple Canon Lenses, with and without grip, with multiple CF cards.
Bit the bullet, spent $65 to send it to Canon, they wanted $198 to diagnose and repair the body, and $128 to diagnose and repair the lens (85 f1.8 was the worst focusing).
Acted up on 5/11
Sent it off on 5/15
Got it back on 5/29, working perfectly (arrived on 5/27, couldn't pick up earlier).
There wasn't much definitive in the work order, but it looked like some electrical components were replaced, and the autofocus was adjusted.
All this with only 33k actuations, and 1 yr 2.5 months of ownership. Bummer, but I'm shooting again. Will be investigating a backup soon.