I ended up trading in my old PSP for the newer one, I just love the newest ones look. With the focus of, I guess in my eyes, of genres that the DS seems to lack, it has allowed me to keep on playing my PSP. I love Disgaea Afternoon of Darkness, Tales of Eternia, Yu-Gi-Oh GX Tag Force 1, 2 (and soon 3), as well as a few other games (Justice League Heroes is amazing).
I own both PSP, and have owned 3 DS systems (they keep breaking...,) now I have a Cobalt Blue DS Lite. Ultimately I just have DS cause of Pokemon Diamond, Metoes, and Pokemon Mystery Dungeon. And with maybe a Golden Sun DS and a few of the DS brain games, thats really all that keeps me holding onto the DS..
I love my PSP more though, graphics are ballin and the games are quite quite quite lenghty and fun for RPG.