A couple months ago I very nearly switched to a GH1 when they were available through Panasonic for $375, as it would have better suited my travel plans and my desire to start working with video. Missed out on the deal pricing, sadly, so the K-x stayed.
Last fall I almost switched over to a Bronica medium-format film setup. I was looking for a change of pace, really. Eventually I just changed the way I shot with my K-x and have no further complaints. I really would love to work with MF film sometime, though.
I had plans a while before that to switch to a Nikon body with one of those great DC lenses and a cheap AF fast 50 to better suit the portraiture and band photography that was supplementing my income at the time. Getting laid off from the main job complicated the situation and it never happened.
The Fall before that I switched from a Canon 40D+85 1.8 (no other lenses, really) to the K-x+kit for travel purposes.
The Spring before that I switched from a K20D to the 40D exclusively due to my desire to work with that lens. It was fun.
I bought the K20D about a year and a half before that to replace my aging Olympus E-330, which was getting pretty beaten up. The K20D was all the right features at precisely the right price.
I switched to the E-330 two years before that because its dwindling stock was the cheapest DSLR I could find at the time. I was switching from Olympus's OM film cameras.
I guess I've done my share of switching. I think one of the biggest myths is that switching brands will always cost you more money. Most of my switches have broken even and in one case I even came out $100 ahead. Due to the peculiarities of SLT design being particularly suited to some specific types of work I'd like to do in the near future, an A55 is likely to be my next camera. I might even stick some m42 takumars on it.
Brand loyalty is overrated. You can always go back if you don't like it, with no big loss if you plan well.