The Canon EOS 7D is the current "state of the art" APS-C crop sensor DSLR. Within the Canon EOS lineup it represents a new level of camera positioned between the "prosumer" APS-C sensor equipped EOS 50D and the "professional" Full Frame sensor equipped EOS 5D MkII. In many ways it's more of a 5D MkII squeezed into an APS-C body than it is an upgrade of the 50D (which will presumably appear at some point as an EOS 60D).
With increased resolution, lowered noise, HD video, a totally new AF and metering system, a blazing fast 8fps continuous shooting rate, ISO from 100 to 12800, a large image buffer, UDMA mode 6 compatibility, built-in wireless flash control and an integral electronic level, it packed with enough new features to keep almost anyone happy!
Compared with the, the EOS 7D is about $1000 cheaper. While it may not be able to quite match the 5D MkII in terms of ultimate resolution and high ISO noise performance, in all other respects the EOS 7D seems to match or beat the 5D MkII. Compared with the EOS 50D, the EOS 7D is about $700 more expensive, but it outfeatures the 50D in just about every aspect and includes broadcast quality HD video. Of course the 5D MkII has a full frame sensor and that has several advantages over APS-C. First a full frame sensor may better "match" some full frame lenses. For example the excellent make sa great wideangle to short telephoto lens on a full frame camera, but when used on an APS-C camera it looses its wideangle capability (24mm on APS-C gives the same view as a 38mm lens would on full frame). There's also a DOF difference. The larger the frame size the smaller the depth of field (for equivalent views and the same sized prints), so a full frame camera is capable of better isolating a subject via the use of a small DOF (i.e. a fast lens used wide open).
I currently own an EOS 40D, having decided not to upgrade to the EOS 50D because, for me, the performance improvement, though real, really didn't justify the expense of upgrading. The EOS 7D is different though. It certainly has enough new features that upgrading from the EOS 40D, or even the EOS 50D, to the EOS 7D seems like a justifiable move.
The new EOS 7D would be an excellent choice for any serious photographer and will certainly appeal to sports and action photographers who can benefit from the 8fps continuous shooting rate and totally new AF system. It provides a very cost effective alternative to the new EOS 1D MkIV for sports shooters, at a cost which is about $3300 lower ($1699 vs. $4999).
The new looks like it would be an ideal match for the EOS 7D if you're looking for a general purpose "all around" lens. In 35mm full frame terms it would have coverage on a 7D equivalent to a 24-136mm on a full frame camera.
Well, updating this page in December 2014, the EOS 7D has been replaced by the even better (and not much more expensive) . However the EOS 7D is still a very good camera (I'm still using mine) and you can find some good used 7D bodies at very reasonable prices if you look around.