People with really low milage bikes think they're still good as new. After 3 or 4 years, I tend to disagree. Battery, tires, hoses, fork seals, carbs, etc are the obvious things to look for. The not so obvious is this...if there is any kind of manufacturing defect with the individual bike or known issue with the model/year they tend to appear in the first few thousand miles. Ideally it all gets sorted out under warranty, if not it can get expensive. I don't know much about the yzf600, it very well could be a bulletproof design. If it were me, I'd be more comfortable if it had a few thousand more miles. My $.08.