As of my writing this, Game are taking pre-orders for the PSP Go at £230 pounds, while a PSP 3000 will set you back £140, including a bundled game. So what do you get for your extra £90, besides a lack of a free game?
Well, you get a smaller and lighter PSP, 16GB of flash memory and a download only distribution model for games. Now as far as the smaller and lighter part goes, only you know whether or not you need it enough to spend an extra ninety quid. But the rest of it? The PSP Go is a rip off of the highest order.
16 GB of internal flash memory is nice, but if you really need storage space, dabs will sell you 4GB memory stick pro cards for £17.50. That means that a PSP 3000 with 16GB of memory and a copy of  Tekken: Dark Resurrection will cost £210 pounds.
Looked at like that, the Go may not be too much of a bad deal. A £20 pound premium, and no bundled game, in exchange for the small, lightweight version.
Except that the PSP Go lacks a UMD drive
UMD might be rubbish format, but there thousands of used UMD games sitting on the shelves of Gamestation, none of which will run on the Go. The only way to buy games for the Go is via the PlayStation Network, as digital downloads. Maybe that's not a problem for you ( it is for me, but that's another story). Maybe you only want to download games, maybe you have been eagerly awaiting the dawning of the digital download era of game distribution. All well and good. but not a reason to buy a Go. All the existing models of the PSP will have exactly the same access to the Playstation Network, and will be able to download exactly the same games, as the Go.
The problem with the Go is not the price itself. After all, Nintendo just released a minimally improved version of the DS for an extra £50. The problem is that, memory and size aside, the PSP Go is actually inferior to a PSP 3000. The Go is stripped down PSP 3000 with some flash memory bolted on. They should be selling it for less than the other models, not more.