OK, I had a Canon EOS 400D that had served me well for nearly 3 years (and I had a 300D before that) and was looking to upgrade it, but I couldn't decide between a 550D or a much more expensive 7D. Then the 60D was launched and from the reviews I read, it filled the gap perfectly between the two. As ever, launch pricing was really toppy at over £1k but I took the plunge just before Christmas 2010 and bought the 60D (with the 18-55 IS kit lens) for a great price of £799.
It's still fairly early days but so far, so good. The camera is a dream to use, images are razor sharp. Handling is easier than the lower spec DSLRs in Canon's range due to the fact that the 60D is a slightly bigger, bulkier machine but without this being a negative. If you are familiar with a Canon DSLR, all of the controls and features are logical and easy to use without having to trawl through the manual. The tiltable screen is a work of genius, especially the fact that you can store the screen facing into the camera for even more protection when not in use. You can also tilt the screen and take shots based on the screen view if, for example, you are taking shots with the camera held above your head to get a clear view.
I primarily use my old 28-135mm IS USM Canon lens and image quality is fantastic. I have also bought a Canon 70-300mm IS USM zoom and again it seems to produce great results. I am using Class 10 SDHC cards (whereas my previous 2 Canon DSLRs used Compact Flash) and the speed is lightning fast - I have bought a couple of the Transcend ones from Amazon and they seem to do a remarkably good job for a lot less money than the competition. Only time will tell if they prove to be reliable...
The only downside is that my camera was supplied with an old version of firmware installed (v5), which needed updating (to v8) to cure a quirk with over-exposure when using certain lensses (and the two lenses mentioned above were included in this list). I went through the whole firmware update process in a mild panic but it was a remarkably pain-free experience.
Overall, the 60D is a great mid-range camera and a worthy upgrade from my 400D. The 60D strikes the perfect balance for me in that it offers more functionality / flexibility than the 550D but without the complexity of the more advanced 7D. I am fairly loyal to Canon gear but I did look around at the Nikon equivalents before making my purchase - however, I ruled out Nikon as you just seem to get more for your money with Canon. Also worth saying that the lens/flashgun I already had are compatible with the 60D. The next step for me is properly testing out the camera's HD video capability.