Yay! Flamebait!

There is a small minority of Pentax, Olympus, and Sony users. I don't know much about Oly or Sony (I tend to stay far away from Sony products), but Pentax makes a pretty nice camera. My friend has one, and it has some pretty cool features. I would definitely say the image quality out of the Pentax is better than my Canon.

The big disadvantage of any camera other than Canon and Nikon is the small amount of used and third party products. Sigma, Tokina, and Tamron all make lenses for the big dogs...and they don't always make compatible versions for the others (not cost effective).

Sony is especially notorious for designing their products so that ONLY Sony accessories will work with it. Combine that with their ambitious copyright agenda...