So I borrowed a friend's PSP Go to get it up to speed. By that I mean get lots of demos and free swag in general onto it.
Personally, I'm no fan of the Go. It's overpriced and under featured. It has more hard drive space and a nicer screen, but at the cost of UMD functionality, which renders most of the PSP's game library useless to a Go owner.
Secondly, all the DLC features of a Go are easily accessible with a regular PSP, from the original 1000 to the current 3000 model, especially thanks to Sony's almost too-frequent system updates.
So why Go? I'm not sure, but you can draw your own conclusions, since I took a few comparison images.
My PSP 2000(unhacked, mind!) is on top, my friend's Go is beneath.
Running the Warhammer 40k Squad Command demo:
DJ MAX Clazziquai Theme:
In addition to the brighter screen and lighter weight, the system also has fairly better sound.
However, it lacks some shortcuts of the normal PSP. I couldn't find the 'Home' button, which I've gotten used to. The analog and buttons in general are also very condensed, found closer to the center of the system rather than at each end.
The PSP Go could be a hit with the I-Pod generation, but I think it's too little, too soon. And judging by the Go's reputedly dire sales, the consumers seem to agree.