First point in buying a camera is figuring out whose mount you want to shoot, and why. So here's where I was, and where we are now, regarding shooting:
so, why sony?
I chose Sony on recommendation of a camera-shop salesman. Holding the a350, I really liked the feel of what they were doing, and was told they'd bought in big to become a player in the DSLR market. It had a few major advantages over the Canon/Nikon versions - it was a little cheaper, just as well made, it had a better live view function (a big deal at the time), and the body was stabilized.
Digital stabilization allows hand-held pictures to be more easily done, when otherwise movement would be too great or light is scarce and you'd need a slow shutter speed. Canon and Nikon are lens-stabilized - you're paying for it every time you buy a new stabilized lens (or do without). Sony gives it away in the price of the body. Which leads me to the other advantage: Minolta lenses.
Buying a new body for old lenses sounds odd, but lenses are a much better value for longtime shooters than bodies. Two year old cameras aren't obsolete, but new cameras do so much more and aren't much more expensive - if you stay with it, you'll buy a new body in five years to use with the same lenses. Sony bought Minolta, and so therefore a lot of their lenses are the same as the old Minoltas - but more importantly, all Minolta autofocus lenses fit. I envisioned a fleet of inexpensive Minolta lenses (with the image stabilization) instead of one lens-stabilized Canon zoom.
So, why not Sony?
First, their new lens selection is lessened (though like most shooters, a specialty lens or two, if you get it, will start out being made by a third party like Tamron, Sigma). Minolta lagged in the digital realm, and Sony's behind the curve. So, every lens innovation is a leap forward, compared to a stable of Canikon lenses.
Second, they've mostly pushed entry level. Their full-frame (35mm sized sensor) cameras made a big leap forward, but no replacement for those (or the digital size pro camera) are in sight yet. So, looking for the latest and greatest in studio camera or high speed sports camera leaves you looking elsewhere.
Third, no HD video. I don't need to buy a new camera for it, but buying a new camera, you'd want it. They're working on it, but the others have it.
So, who else then?
if you made it to the point of considering Sony, you know Canon and Nikon, the popular guys on the block. More expensive, and the lenses are stabilized, not the bodies (and most of us will handhold most pictures). Sony's not the only one with in-body stabilization - Pentax is the 4th DSLR brand, and their latest offerings have stolen some market share from Sony and Canon.
Make no mistake, though, there are some differences but just research, get a good deal, and make sure you find a way to hold the model you're buying in your hands first.
At this point, Canon's who you want to go to, if you want the fastest lenses (85/1.2 and 50/1.2, for instance). Nikon seems to have a little better quality. Both currently have HD video in their bodies, and Sony doesn't (they're working on it, and like Live View hopefully they get it right in ways the others won't).
