I say 2.40, which added trophies and in-game XMB.
I don't use the trophies at all right now, as I have no trophy-compatible games, but it will add replay value to the games I plan to buy in the future (LBP, BioShock, Resistance 2 etc.)
In-game XMB, on the other hand, is incredible. I use it all the time. It saves time switching games and allows me to use the XMB (at least for adding and messaging friends) without having to quit my game.
They really need to work on improving it in future firmware updates, allowing you to tweak settings (if something stops working), visit the playstation store (just convenient), browse the web (look for hints and walkthroughs [if you say you don't need one, please, try Ninja Gaiden Sigma]) and eventually, even play videos (pass the time when things are loading for a long time, or in MGS4's case, installing).
They also, imo, need to add In-install XMB.
(Former) Lead Moderator and (Eternal) VGC Detective 
