don't currently ride bikes fella but I'm definatley getting one of these as my first bike. Saw one in manchester parked up and it looked really nice. Ok it's not a 'big bike' but as a first bike it's awesome. Insurance quote on a 4 year old 660 ninja couldn't get one below Â£1200, one of the 250r's it was only Â£400.
Trust me, you'll get bored of the Ninja 250 within about a year of owning it. Resale value wont be awesome either. Yeah if looks are what you want then go for it, but I think you'll see through all that after a while.
Personally i'd reccommend a restricted version of another bike, maybe a 400 import. Small enough to be manageable, fun enough to play on regardless of BHP, plus u can de-restrict in future and get straight on a bike with more power that you're already comfortable and familiar with.
Edited to add: RVF400. makes the 250 Ninja look like a reet turd.
Personally I would recommend getting an older model and not being too fussy. Whatever you get at that level you will want to trade up as soon as you can. Buying used means minimal loss when it comes to reselling.
Unless you are a girl or very small framed, the physical size of the bike will be as much of an issue as the lack of power. Big blokes look daft on tiny bikes and comfort over distance becomes a big problem.
If its a first bike I wouldnt recommend a sports model anyway. The plastics are expensive when you drop them! Swallow your ego and look for a naked bike or trail style bike until you have the experience and can legally ride a full size bike. By then you may still want a sports bike but may have decided to go another route.