Pros: D90 adds a faster face detection to its Live View, Continuous shooting 4fps
Cons: The lens seems just slightly less sharp than the kit lenses from Canon
I really enjoy shooting with this camera; it's comfortable to hold, and the control layout and navigation should be immediately recognizable to anyone who's shot with a Nikon dSLR recently. If you're making the switch from another brand, there might be a bit of a learning curve; for example, Nikon puts the white balance, ISO, and quality buttons to the left of the LCD on its cameras, while other manufacturers tend to place them under the control of your right hand. As I complained about with the D80, I wish they were more easily identifiable by touch and the labeling a bit less cluttered.
Like the newer Canon EOS 50D, the D90 adds face detection to its Live View repertoire--part of the enhancements enabled by a revision of its Expeed image processor--though it maxes out at five faces. The FD supplies data to the camera's face-priority AF, and Nikon has integrated the FD information into its automatic scene recognition algorithms to help with metering and AF. In practice, it doesn't seem to make much difference, either in speed or portrait quality, over wide-area AF; both of those two AF modes are significantly faster than normal area AF in Live View, however.
Ultimately, the Nikon D90 gets high marks because it's a fast camera that delivers a great shooting experience and first-rate photos for the money. If your budget can't stretch quite that far, the D80 remains an excellent deal at its price.