Ok, so imagine instant messaging, but have it so you can have multiple folks in on the conversation -- so, like a chat-room (or so I presume, since I've never chat roomed. Or is it room chatted?). Now, have it so when you scope out a particular room (here, they're called "Waves") you aren't just seeing a live-feed but can also see what's been said earlier. Also, it's not just one bit of text after the next bit of text (here, the bits of text are called "Blips"), but you can instead hang a comment off of someone else's comment, like here in LiveJournal. And if need be, you can go back and edit those previous comments of yours.
Take that (with real-time typing display) and have the database of Waves be searchable so you can look for a particularly titled Wave or a Wave that mentions some particular topic. Obviously, one can also set a particular Wave to be private, so only invited folks can scope it out and/or talk on it.
Oh, and Google Gadgets can plug into it, so one can have a thing that inserts a poll or tosses in a Google Map reference or whatnot. This bit'll be handy for online text-based role-playing games, since then one can work up and plug in a Gadget for dice (unless, of course, one is doing it with some DM/GM sort of person who's making the die-calls). The RPG aspect also is what led me to posit my first suggestion to the Beta-testing board (at least, I -think- it was submitted): Being able to see the earlier versions of an edited blip. That way, Evil Larry can't go back and edit an earlier blipped-pose so he can say, "Dude! I totally had a lit lantern out already!"