Sony have deliberately locked the PSP's operating speed at exactly two-thirds of it's actual potential. They have an extra fifty percent of it's current performance ability simply waiting in reserve to be unleashed at a later date.

[...] Why would Sony choose to cripple their own hardware? Well, the most obvious answer is that they needed to maintain an acceptable battery life. In the lead up to PSP's debut, it's battery duration was often quoted as it's single biggest potential problem. Had they launched the PSP with games running at a fully unlocked 333Mhz, the battery could have been dead in less than two hours. That just wouldn't do.

[...] The tangible difference in the games should be very noticeable. Example: Right now, the PSP has a maximum fillrate of 444 Mpixels/sec. After the restrictions are lifted that will become 664 Mpixels/sec. Games will be able to feature more complex models with higher polygon-counts, more fluid frame-rates, better physics, you name it. We are talking about an across-the-board fifty percent performance increase after all. PSP's hardware supremacy over the PS2 should become evident.