Everyone I know who owned a PSP ended up replacing it for a DS. The DS just makes a better portable with games suited for playing on the go in short amounts of time.
Very true in my case. I play the DS a lot more than the PSP. However, the PSP is a quality machine that has a decent amount of playability.
DS also allows free acess to wifi at all McDonalds in Australia. Its a deal bewteen Telstra, McDonalds, and Nintendo. Saying this though, i still prefer the PSP