there's already two really good PSP threads here on the board, as well there are several hands on reviews all over the 'net which would answer all of your questions.
I do own one already, since Xmas... it has easily become my favorite system ever, and I have owned almost every system released since NES. Even though I bought one right after release and got gouged like a mofo on the price, I still feel it was worth every penny.
To answer your questions:
1. It does scratch relatively easily... this is easily one of my biggest gripes with the system. Since it doesn't fold over, the thing gets dirty very easliy, even in the slip cover case that I got in the value pack... so you end up cleaning it a lot, or at least, I do. I have only ever cleaned it with a special, soft, lint free cloth designed for cleaning eyeglasses, and using a special spray also for the same purpose, and still, I have accumilated a couple hairline scratches on the thing. And I am SO careful with it... for the price I paid you can believe I treat the thing like a fine piece of art.
2. Not nearly as bad as Nintendo fanboys would like you to believe. Claims of 3 hours and under are BS. Running Ridge Racer (supposedly the most graphically intensive game on the system) at full brightness (which you will rarely ever need or want to use) with full volume off the internal speakers, average is about 3.5-4 hours. With medium brightness which is more than adequate in most conditions, you're looking at more like 5 hours. With less intensive games, upwards of 6 hours. And before any fanboys would point and say "hah see the DS is better!" I have two DS's, which I bought for me and my wife, and both of us played the hell out of mario when we first got it... and guess how much battery life we averaged per charge?? 5-6 hours.....
3. yes and no. it's hard to get used to, and since it has a small range of motion, it can be very sensitive. It is TRUE, FULL analog though, some people were saying it wasn't. I've seen this when using it to control the camera in MGA and Golf.
4. RR runs very smoothly... most games do. I have noticed a bit of slowdown in MGA when there's like 5+ guys on screen in complicated areas... odd because RR looks much better and seems to use many more poly's than MGA, and RR never slows down.
If you're interested, I'm actually going to be selling a Japanese PSP value pack (comes with memory card, carry case, wrist strap, headphones) for $250 + shipping. It is used but still in fantastic condition.