I use PSP plugins for: swapping the X and O buttons in the OS because that's what JP games have gotten me used to and it's awkward right now on the PS3 (why enable JP language support without swapping the buttons for it >_>); taking screenshots; power save; the mentioned CXMB. I'd use the save state one if it worked on the 1000s, because there are way too many games on the PSP, not to mention PS1 games, with save points way too infrequent for a portable.
Store... a quick google has links to psn psp/minis piracy. Don't know if that spells trouble for the PS3 PSN titles though.
Online... not big on it either. Though Sony seems to ban people very rarely, even for cheating (plenty of complains about that on forums). Maybe they'll have to tighten up the moderation.
