Well I'll try to avoid the FanBoy type comments and give an opinion on my PSP.
I got it a Christmas and haven't stopped using it, I mainly use it for games (Burnout Legends, Hotshot Golf, Worms, Megaman Powered Up, plus many others) but recently I've also been using it for videos on the move.
There used to be comments saying that it had a poor selection of games with the majority of them being driving games, I'd say this argument can now be ignored as the PSP as a huge selection of games across many genres.
Network play is an ease, I've had loads of fun with this as 7 other guys in our department now have PSPs.
I'd say take a look at the games that are available for it, if there’s something you want to play and it's not available on your DS (or the PSP port is considered a better version of it) then invest in one.