After riding the track pretty hard on Saturday I decided it was time to check my valve clearances for the first time since getting my WR in November. I've got about 750 miles on the bike and have been changing the oil about every 150 miles. After break-in, I have used nothing but Royal Purple synthetic. Popped the valve cover off and couldn't believe how clean the top end was. Cam chain was tight and the cam lobes looked like new. Got out the feeler gauges and checked. All the valves were within spec. The two outboard intakes were close to the low end of spec, but not by much. The exhausts were right in the middle. The whole process took about an hour so I decided to check my brother's '03 YZ250F, as well. He doesn't ride as hard or as much as I do, but his bike is older and has more miles. His valves were also still in spec, but a litle bit closer to the limits than mine. Just what I would have expected. Anyone that says the 4-strokes are too complicated or require too much labor probably has a fear of wrenching on their bike. Change the oil regularly, watch the service intervals, and you should be fine.