I understand where people are coming from when the say "you'll be sick of the 250 in a week" but I would never say it's a bad idea to start off on one.
The Ninja 250R has been the default choice for years and now with the 2008 update it's even more popular but the price is getting to the point where it's not really that great a value.
What I think made Kawasaki suddenly update the 250R is Hyosung coming into the U.S. market with their GT250R and GT650R. They are better looking bikes -- even after Kawi's update -- and now for the 2010 year have Direct Fuel Injection. They handle better, get better MPG and have a better dash and are the size of real 600cc bikes and have the aggressive body position. There are some who question reliability because it's less of a known brand but I know people who've been riding them for years and they seem fine, 2 year warranty as well.
Kawasaki on the left, Hyosung on the right.
Not bad at all for a $4,200 MSRP. Also, Hyosungs get you ridiculously cheap insurance. One 40yo male on youtube is paying $98 a year for the 600cc through progressive.