Once again many of us are giving in to the sensationalized media of the PSP. My rule of thumb is if Sony says their system is capable of something, or releases specs, I downgrade it by 10% because they're geniuses and propoganda. Make the people believe and they'll consume.
The issue that I believe should be at the forefront is definitely durability. In my opinion once you look past the graphics, design should really be the issue at the forefront. Aesthetically, I believe both companies did a very a good job at what they set out to accomplish. I've really heard both sides of the coin when it comes to design. Some like PSP, some like DS. Aesthetically, I think the PSP slightly edges the DS, but that's not my concern.
Look at the durability of both systems and compare. DS: Clamshell design equates to protection of the system's vitals, secure cartridge slots mean no loss of gameplay if dropped or shaken violently, when closed the thickness of the unit is increased making it a tougher system overall.
With the PSP, the whole system is exposed. The screen is bound to take heavy damage. I remember complaining about my GBA screen getting riddled with scratches, take that to another extreme with the PSP. The analog joystick has a huge risk of getting damaged and possibly malfunctioning if dropped, the lack of thickness and extreme lightweight could make for a fragile system, when dropped, the UMD might be damaged in the process.
I remember having CD players where if I'd drop it, the player would sometimes open and spit out my CD, causing irrepairable scratches.
Portables NEED to be durable because they are being taken everywhere you go, everywhere you need to play, whether it be an airport terminal, walking to the store, riding the bus...and in the past, Sony has a reputation of making their products rather fragile while Nintendo has a legacy of keeping consumers satisfied with durability. I've heard a lot of stories about GBAs and GBCs being left out in the rain, snow, put through the wash. You name it and they survived.