Here are my overall impressions of the 7D. Keep in mind, I started out with a <2 MP Casio P&S, then a 5 MP Sony P&S.
My dSLR history followed by starting with a Canon 350D (8MP), and then a Canon 40D (10MP). The biggest upgrade that I felt was actually the introduction of the back dial. I shoot nearly exclusively in manual exposure, so having a dial to separately control aperture and shutter is huge to me. Viewfinder and LCD screen enhancements were the next biggest upgrades. The new AF and shutter mechanism were enjoyed as well. Of course, magnesium body and allthat too.
The 7D is a great camera. I think it's a milestone camera. Certainly the best APS-C DSLR camera that Canon has put out, and bridges the smaller sensor camera into the realm of professional.
I used to be worried about increase of noise with smaller pixels (a consequence of ever increasing MP counts), but what I found was that the noise (note I shoot JPEGS and often have NR set to standard) at the 100% pixel level was about one stop better than the 40D. This was remarkable in itself, but the biggest deal was that the increased MP meant that when I view images at a reasonable size, noise was even less of an issue. And when no DID show up, it felt much more 'film' like.
On the 350D, Iso 100-400 was the standard. Iso800 was emergencies, and 1600 was nearly a no go. On the 40D iso 100-400 was still the standard, but I'd be willing to go to 800 if need be. iso 1600 for emergencies, and 3200 was pretty bad.
On the 7D, I actually use 200-1600 as standard. 3200 if I have to, 6400 for emergencies, and I rarely shoot in 12,800. But that's remarkable. It really does change your photography.
The other thing I noticed about the 18MP is that it does resolve more detail. the jump from 10MP is moderately significant. I can get near macro-like detail out of my good lenses, and my macro has become nearly an entirely different beast altogether.
The AF system is robust, and thrills the tech gadget geek in me. I know Nikon have been enjoying the LCD overlay style for sometime, but I'm pleased Canon are following. I have had no problems, and I invite the vast arrange of features it supports. I don't do many tracking shots, but I've seen it working and it does so very well.
I love the gorgeous screen. As a JPEG shooter, I chimp a lot, so having a great hi-pixel screen is great. The user customisability of this camera is one of the best too.
Video is great, but as I found out, video shooting on an SLR is something you really have to dedicate effort to. I haven't figured it all out myself. You'll need more gear to make the most of it, the first being a microphone (the built-in mic doesn't cut it as it pickup things like the focus and IS). Stabilisation will also be another requirement. If you plan on using it for video, realise that it's not just click-and-go - it's like getting into flash photography - you'll need to learn and practice a lot.
Overall, I think the 7D is above average in all respects and makes it a superb jack-of-all trades camera, sacrificing very little. I haven't used a full-frame camera, but after playing with the 7D, I feel I don't need to. Well, until the 5D mkIII.