I've got a 1999 model (well, ok its a Suzuki Freewind, but it's still a DR650 motor) and so far (11,000kms) it's been great. Never missed a beat and never looked like giving trouble either and I've ridden in everything from desert to highways to snow. Before I bought it, I was actually trying to decide wether to buy a DR650 or KLR650 so I spent hours searching for owners reports on both bikes details any problems they'd had. I found a few for the KLR, but apart from the weeping base gasket on some DR650's it was all pretty good. The only thing with mine is a slight oil leak from the rocker cover. But that only happens when you ride it hard (130kph+) for an extended period of time
The other great thing about the DR is screw and locknut vavle adjusters make it soooo easy to do your own valve clearances.