I've stayed away from digital SLRs (which used to mean single-lens reflex camera, but now just signifies that it's a camera body that can accept standard SLR lenses) because only the most expensive--over $5,000--shoot in 'full-frame', meaning a 35x24mm sensor. Because most DSLRs used a smaller sensor (usually 24x16mm) it meant that the lenses you bought were only useful with DSLRs. Also, it meant many of the plentiful second-hand lenses were not particularly useful.
But full-frame technology is coming down market, and Nikon is leading the way. Rumors of a new D700 are hot right now, which is the more expensive D3 FX (full-frame) sensor in a prosumer D300 body. The camera won't exactly be cheap, but it shows that full-frame is the future and will soon be within the grasp of the general consumer.