I recently bought the new PSP GO! let me do a review here for all you contemplating on buying a PSP.

First things first, the pain of carrying games around with you all the time is gone because the new PSP cannot accept UMDs! this is because all the games are stored on the new 16GB built hard drive. first problem, you only get 14GB because 2GB is already used for system files etc. So thats at least 2-3 games less that you can store!
The new PSP is alot smaller so it actually fits into your pocket, unlike the old PSP which was literally the size of a brick, the new one is also alot brighter, longer lasting battery and faster WiFi. The screen on the new one is smaller but the resolution is the same so no loss of graphics or quality.
The major downfall so far is that all your old games for the PSP is no longer usable of course and the old one doesnt sell for much either so if you wanted to trade in old for new you still have to pay abit for it!
The new one is £224 from GAME, you cant use you student card for discounts though! which was a big let down for me when I found out, its the same price in HMV but comes with a case! haha what a deal!
I got mine from CEX which is £190, second hand but never used, due to people selling them as soon as they get it free with a contract phone, so its practically brandnew.
They take in the old PSP for £65 trade-in which is more than what the other stores take in for, and they sell it cheaper so its the only place to go really.
The other the downside is obviously the games, if you buy games from stores you can get discount from student cards, which was always nice, but now you buy online you cant get any discounts at all! not can you buy second hand games which is kick in the balls!
Good sides are that the new one is really slick and good looking and easy to carry around and also you dont really need to spend money on memory cards.
I dont believe the price will go down too much niether will there be deals because they cant come with games! There is a good deal though, if you own the old PSP then you can get 3 games free if you buy the PSP GO! which is quite a deal before you realize that you can only choose from a selected list.
In conclusion, if you have many games for your PSP and if your old one is not in very good condition then I would stick with it for a while to see how it turns out, but if your a big gadget fan like myself then I would advise to get it since it is nice!