I joined mostly because this place seemed to fit me best.
I've been on reddit for a while and that's initially how I found out about geekhack, but I've already posted more here than I have on /r/mk.
It could have something to do with being a kid in the '90s - all I did back then was chat and post on all kinds of forums like this one.
I lurked both places and this just seemed like the best fit for me, personally.
Other people should join because they feel like they would also belong here, and then make a go of it.