Even the President thinks so! In his talk yesterday, he warned kids about Facebook, and being careful what they should post. It’s also what I talk about in my branding and blogging talks, be careful what you post.
However it’s not a permanent thing you can’t get over. At least in the US we are likely to give you a second chance if you post something in appropriate.
Each post, however, adds to your reputation. If you have too many things that show you’re not very responsible, it looks bad.
(cross posted to The Modern Resume)