The longer battery life in the slim is offset by the fact that they included a much smaller capacity battery as the default slim battery. That's partially how they kept the price down. If you put an old PSP battery in the slim, word is the battery life jumps up to 10 hours instead of 5.
The faster loading in later games that make use of its extra memory is confirmed. Just look at the side by side comparison of Crisis Core running on a slim and 1000 model.
I actually prefer the new UMD tray, as I found the mechanics for the old spring loaded tray somewhat pointless.
One of the best things with the PSP 2000 model is that the speakers now face forward instead of coming out the bottom.
I just wish they'd come out with a bluetooth adapter.
Or a PSP2 with touch screen, better ergonomics, clamshell style case that actually protects the screen when closed, etc...