I love it. If you are looking for the most reliable 250f get a yamaha. Yamaha's tend to get more valve life than the other makes, probably because they have 3 smaller, lighter, intake valves. Hondas are known to have valve issues, but it is really over hyped. I think Hondas are more reliable than Kawi/Suzuki, atleast for the earlier models. I rode my bike pretty hard, and put 75 hours on it (all motocross) before the valves started to move. You will get a lot more than that if you are trail riding.
I wouldn't call it "problems." These are basically 1 cylinder formula 1 engines lol. I think the rev limiter is 13,500 RPM. I think a lot of the problems were more of a maintinance issue. The valves have a coating over them, and if you don't clean and oil the air filter often and then engine starts ******* in dirty air it will wear that coating off quickly. Once that happens the valves go pretty fast.