If this hasn't sunken in, yet please take note -- what you do online will haunt you. But it's not just social networks that open sourcers have to worry about.
Participants in open source communities are subject to even closer scrutiny, because employers can simply follow the threads and see how well an individual comports themselves on a list, and what kind of contributions they've made. Sure, it's still a bad idea to brag about excessive alcohol consumption or your sexual exploits on Facebook, but you probably want to watch the flames on project mailing lists as well.
So let me offer some advice to employers and potential employees alike. If you're hiring in the open source community, someone on the hiring committee ought to be combing through mailing lists, blogs, and social network sites to evaluate new hires. And through code contributions, of course, if you're hiring a developer.
A few minutes with Google and some email archives, and you can usually find out pretty quickly what kind of personality your potential hire has, and whether or not they play well with others.
On the contributor side -- I see all too many open source contributors who are too willing to flame first and think later. I'll endorse the contributors who engage in a bit of well-meaning snark now and again, but if a potential hire shows an inability to work with others in the project on the mailing list, it's unlikely they'd be a better bet when hired.
I know my blogs and general online presence has been evaluated when I've been in the hotseat, what about you?