Lately I have been looking at upgrading to a camera giving a bit better quality and low-light performance than my aging SX100, and naturally the obvious choice would be going the DSLR route.
I have mostly been looking at two models, the Canon 450D versus Nikon's new D5000. The Nikon has a lot going for it over the Canon: very good high-ISO performance, viewfinder grid, and 11 autofocus points versus the 450D's 9.
The Canon on the other hand can autofocus with all lenses, EF and EF-S, while not all Nikon lenses have the autofocus motor in the lens that the D5000 needs.
Besides that, the Canon uses the same GUI as my SX100, possibly making for an easier transition. At the moment I'm aiming at the 450D, since it's about 100 euros cheaper than the D5000. Of course I've also looked at the Canon 1000D, but with my ambitions of getting faster lenses the extra autofocus sensitivity at f2.8 on the 450D comes into play. (That and it's basically become impossible to find any 1000D kits with the IS lens; having heard bad things about the standard 18-55 kit lens has made the prospect of going up a notch to the 450D IS kit an overall better prospect.)