I have had a Canon 7D for pretty much exactly two years as of Dec. 11th. I am getting close to the 100,000 shutter actuation mark (I have over 85,000 photos that I've KEPT, and I have deleted at least 12,000-13,000 photos that were obvious rejects or just junk not worth keeping over that time.)
The shutter is rated for 150,000 actuations, but there really is not telling when it might fail. Ratings tend to be conservative, and a percentage of shutters will die well before their rated time. That said, a similar percentage will outlast well beyond their rated time (I've heard of the 7D shutter lasting for several hundred thousand actuations before.)
I suspect my 7D might not last much beyond 200,000 actuations. I use it moderately frequently in extreme situations. It has been to sub-zero (°F) on multiple occasions, in a couple occasions I worked it pretty hard at -20°F with 60mph winds and snow flurries racing down a mountain valley at 11,500 feet, and for the last couple of weeks, I've been using it at -10° to -12° while photographing the night sky (and Comet Lovejoy). You can HEAR when things get really rough for the camera...the shutter starts to struggle, and the whole actuation apparatus sounds audibly under stress at around -10°F. For single stills shots, or shots on an intervalometer, it isn't so bad. The few times I've tried to photograph action, such as BIF, during Colorado's deep December freeze, I can really hear the shutter struggling...frame rate suffers, continuous frames drops, and you experience a negative ramp...the first few shots will be "quick", and the rate of fire quickly drops and inter-frame delay increases after those first couple, until the camera will simply stop, and you have to release the shutter button.
SO...given that I have nearly 100,000 actuations, and I've used it often enough in VERY extreme conditions that would probably shatter a lowly Rebel, I have to say I expect the 7D shutter is very well built and should generally reach its 150,000 rating pretty easily, and surpass it, so long as it is used under normal circumstances and temperatures. If you are looking to buy a camera that has 15-30k actuations, and don't plan to be using it in sub-freezing temperatures (or, extremely hot temperatures, or highly dusty areas, or areas with lots of salt spray) then you will probably be fine. If you DO intend to use it in extreme situations, then I'd look for a camera with fewer actuations...as those 30k could cost you (unless the camera is just an absolute STEAL of a deal.)
