It's not just your own blog or MySpace entry that you need to monitor...
Email from a student who interviewed recently with a large federal agency...
[Unnamed agency] is truly "big brother." My friend has a blog where he posted some stories from our recent Vegas trip (and there is no way they could have found it with a simple Google search of my name). At the end of the interview they showed me that they had printed out the blog.
It was quite a surprise (at least the stories weren't that bad, and they certainly weren't criminal). I was really embarrassed by the fact they found them though, but they assured me they wouldn't affect whether I was hired (mostly because I didn't write them), they just wanted to point out that I need to be careful if I worked there. It taught me a real lesson. I have to be very careful about what might be posted on the internet that has my name somewhere on it.