Five or Six, plus I'm hosting two... (Monogram Mafia II and Diorama Contest).. And one unoffcial one in the Aircraft Hooch that seems to have dies (B-25 GB).
Sadly, I don't seem to make much progress in any of them, hence my propensity for doing cross-overs.. However, as you can see, I've finished three, plus Monogram Mafia I.. I join far too many though, but it always seems like a good idea at that time.. Guess I'm a "25%er"... Means I finish one outta four, lol.. (That might be a generous estimate, lol)
There's a couple that I'm in that haven't started yet, and/or have end dates far enough in advance that I've joined... Frankly, I think that joining all these Group Builds is getting outta hand, lol..
That said though, I think it's a really good way for new members to really get involved with the forum as well.. Many are shy about posting their work, feel that it ain't "good enough" or whatever, when they look at other's builds... Personally, joining a GB as a Nugget-member is a great way to build up confidince, add skill-sets, learn how (and where) to research, learn new or different techniques, pick up a few tips and tricks, and generally feel part of something, a team, and experience the comraderie of the group in a "Private" environment, where everyone's starting from box-opening on a particular kit or theme...
Back on topic, I do try to only join builds that feature kits I have on-hand though.. I TRY not to join a build that requires me to buy yet another kit (Although I still did it, dammit, and just last week... Thanks a lot, Manny)... But sometimes the theme is too enticing, so it's "C'mon Ebay!"... (Manny, thanks again...)
Ah, well.. As long as my wife stays outta the War Room when I'm working on one...