My PSP-2000 lasts a good 3-4 hours before needing a recharge, and I always play games at max screen brightness. I also never play UMD movies, and I never have the WLAN switch on.
The time varies largely with the game -- older games clock down the CPU of the PSP to 222 or 277 MHz, and newer ones run it at a full 333 MHz, which influences the battery life alot. The PSP-2000 runs a good bit longer than the PSP-1000, on the same battery, in my experience, so losing a bit of time on the PSP-3000 (relative to the 2000), for even better color and contrast isn't a big deal, IMO.
Besides, the PSP-2000 comes with a wimpy 1200 mAh battery (it uses a LOT less power than the PSP-1000, or at least that's my experience). Sony themselves sell a 2200 mAh battery, and you can get batteries for the PSP with up to 3600 mAh.







