..is there such a thing? Would it be terribly hard to make?
I've got my guild set up at GP with some functionality provided by RPGOutfitter and I'm pleased as peach.

Latest addition was a " href="http://www.tsviewer.com/">Teamspeak viewer that allows the users to see whoever is logged on to the TS server. I'm sure our memebers will be logging onto the webpage more frequently to check this one. This service got me thinking, is there an addon out there that harvest a list of online guildmembers and automatically upload the .lua to a central db for publishing?

I sure as heck would love to see it incorporated in GP, but I realize it would require a bit of development. But I'm sure it's feasible, or?

Yes this would be a nice idea.  It should be possible.  There is a application called Xfire which is similar to MSN Messenger etc i.e.   its main function is a chat/messenger service.  But the difference is that its aimed exclusively at gamers.  I use it and I can see not only if my friends are online, but which game (and which server) they are on.   Now Xfire also give you a signature you can add to posts that shows your online status etc.  So in theory, you could create a freeform box for all of your guildies signatures and it would show who was online and who wasnt etc.  Very rough and ready, but a start.

http://www.xfire.com/

Mark