I had an 02 Rev for about 6 months, then got a new 04, and hopefully tomorrow or Saturday a new 05. So I am Beta mad.
They are brilliant bikes, I've had monts and gassers before but nothing compares to that smooth engine and soft suspension and reliability.
I have had no problems, only a leaky carb on the 02 which was fixed by Lampkins.
A couple of guys I ride with have had stator problems but was sorted under warranty. I have had no problems with mine, just simple maintenance, stand and ride.
I would say the 270 is slightly smoother than the 250 and has a little more power lower down. I am not a brilliant rider so power aside I go for the 270 because of the extra smoothness.