Conclusion
It is obvious right from the beginning that the 60D is a new class of camera in the Canon line up of DSLR and not really a direct replacement for the 50D. Compared with the 50D, it does offer some new features, but some features previously on the 50D were also taken away at the same time. Purely on image quality alone, it is certainly a step above the 50D, but is also comparable with the much more expensive 7D. But the same can be said with the cheaper and lower end 550D as well. Since the 550D basically shares the same sensor with the 60D and 7D, the 60D offers no advantage over the cheaper 550D.
The 60D offers a set of very nice feature upgrade over the 550D and for x0D users looking to upgrade to a higher end camera, the 60D is a sensible and compelling choice, which is market that Canon is obviously aiming the 60D at.
However, whether the 60D makes a good upgrade for previous x0D users is a more difficult question to answer. For older x0D users like the 20D and 30D, the 60D does offer many feature upgrade with a higher resolution sensor that also offer better image quality at high ISO. If you can live with a smaller, plastic outer shell body (though a very high quality plastic body shell), then I think it is still a good and viable upgrade option. It is also selling at a price that is significantly cheaper than previous x0D and that will certainly ease the pain of upgrade.
For 50D users, it poses the most difficult question. Although the 60D image quality is a bit better than the 50D, especially at high ISO and it also offers movie mode, which the 50D does not have. The 60D also have some significant features missing compared to the 50D. 50D users looking for a real upgrade may look at the 7D instead, but the problem is that the 7D is significantly more expensive than the 50D, and maybe out of the budget of quite a few 50D users. I really have no answer for 50D users. I think their choices and options for upgrade within the Canon DSLR product tree will continue to be rather difficult for the foreseeable future.
I think it is a pity that Canon decided to leave out some features from the 60D like white balance display in the top LCD, direct button access to white balance setting and AF microadjustment just to name a few. I think most of these feature would add very little or no cost manufacturing the 60D and will definitely make the 60D is even nicer camera to use. I believe that the decision to leave out these features is purely an artificial mean to separate the 60D from the higher end 7D.
Overall, I still think the 60D is a very good camera and fits in very well in the new segment of market that Canon is aiming it at. If the budget is right for you, I have no hesitation in recommending the 60D.