Its harder to develope good correct riding skills on a bike that has the power of a 600cc and up.
Let me begin by saying I love this forum above all, and I respect others opinions of the ninja 250 however I have to respectfully disagree.
Perhaps I can disagree because having owned several motorcycles ranging from 250 cc to 900cc and taking my best friends busa out every other weekend, I can speak from experience.
The ninja 250 is an awesome bike. It has been perfected over the past 10 years. There is no other bike that has the performance capacity this does.
What happens is some people assume that the bigger the bike the better the rider. Unfortunately, that can go both ways. As a beginner, if there is truth to that statement, then you should stay away from the larger CC's cause you will most likely kill yourself. If there is no truth to that statement, then you can take a 250 and keep up with anyone else anyway as you become a better rider. How?
When I had my 250, I rode with a group of about 12 guys, bikes ranged in sizes but the average was probably 600cc. My riding skill allowed me to easily keep up with them, at any time, whether on twisties (where I could always take them) or on the highway (sure they were quicker but not leaving me in the dust)
The 250 has an awesome powerband at 7k rpms and redlines at 14k. Its 0-60 is faster than any sports car on the road and it will hit 100mph without any trouble. Does anyone really need more performance than this?
If you can learn how to ride on a 250, when you upgrade them bike, which you will do at some point, you will be a far better rider than any of these knuckleheads that get into something larger.
They really have no idea what they are getting into. When you sit on a machine that is capable of lifting the front tire off the ground in 5th gear doing 20 mph (little experiment on the busa) that type of power and speed is insane and totally not necessary.
So, in closing, I would recommend getting the 250 as a beginner (and even most "experienced" riders would benefit by it) and see if riding is for you before making such a huge commitment. Some people dont like riding after all, look at all the classifieds in your local paper for harleys for sale. Most are brand new because people go all out for the lifestyle yet find out that they hate it.
Dont buy a new one, dealers kill you with their doc and prep fees, even thought the msrp is way reasonable. You should be able to find one that is less than two years old, low miles and in great shape for less than $2500, easy. When done, sell it for the same amount.