It's been so long that we'd completely forgotten that the PSP was underclocked at release. With Sony's 3.50 firmware update, the PSP's processor will be upgraded from 266 to 333 MHz. This slight boost in processing power will offer developers a bit more power to design for, though as most of our readers know, that's not a massive speed bump.
Originally, most speculated that the system was clocked down for battery life. Kotaku speculates that the processor bump supports the prospect of a bigger battery and/or the rumored new PSP system. And we'd have to agree.
PSP Speedboost with 3.50 Firmware [kotaku]