I said it before, but I will say it again. In my opinion what made the original Playstation and the current Xbox so popular was that they could be modded. Being able to tinker with a device and hack it adds much more appeal compared to closed systems. This is also what will make the PSP outshine the DS over time.
If you are looking to run homebrew applications on your PSP (who isn’t) then Make has a wonderful tutorial showing you how its done.
Now just give me an attachable keyboard and easy to run Linux OS on the system and I will be set.