I bleed blue, so I am biased.
Anyhow, I just sold my 04 YZ250F about 6 months ago. Bought it brand new from the dealer and I really can't say anything bad about it. I raced MX (C class) on it for 3 or 4 years, rode trails off and on, and never had any major issues. I always rode with a clean air filer, and changed the oil every couple of rides. It never needed rebuilt, the valves didn't need adjusted (checked every few rides), and it was just rock solid reliable.
I completely agree it wasn't a powerhouse, but it took a pretty good beating while I owned it and never left me stranded anywhere. While I owned it I went through three or four sets of tires, one clutch, a few sets of bars, two sets of plastics, three sets of chain/sprockets, three sets of fork seals....you get the idea. Everything I replaced was a wear item.
Yamaha uses 5 valves rather than 4, so they typically last a little longer before needing a rebuild. All the 250F's are made for 14 year olds...so the suspension will need some work unless you are a feather weight. If you aren't on it already, thumpertalk.com has an awesome forum for bikes.