Hmm. A Ninja?

[Jonno.]

Depends what you want out of it.
Fast compared to a bicycle, yes.
Fast compared to anything else, maybe not.
If you're going to upgrade as soon as you can it seems like a waste of money you lose on resale.

Go test ride a lot of bikes. Not every bike is good for everyone.

[contented]

Wow! Thanks for so many helpful replies, it's given me -and more likely than not my fellow keen beginners- plenty to chew over. I have ruled out a new bike completely due to resale and likelihood of falling off it like a doofus and wrecking it and so I am going to do a tour of the used bike dealers at the weekend to try and narrow it down based on price to start with while I shop for some riding gear.

That picture of the shiny new Ninja really made me grin -I could almost picture meself on it- but sadly reality (Mr. Visa statement) brought himself to my attention not long after and my high and happy mood went down like a sodding lead balloon.
I'm going to have a really good look at everything that has been suggested here, thanks again for the great help.