Bossworld:
Took me about 35 minutes to install the Gran Turismo data from the UMD for some reason (sandisk 2gb gaming edition), whereas it's down on the instruction booklet as more like 15.
Can't see why you'd really need one of this size unless you've got a lot films to watch, or you pirate your games (which i'm glad to see is getting harder - there aren't enough decent games out on the PSP as it is).
Don't forget though, Sony are going to be selling a lot of PSP games by digital download instead of UMD in the near future .
You may need the 8gb (perhaps more) in the near future