Back in the day there weren't the same privacy options as there are now. You used to be able to see anyone in your network's profile (which would be a problem when looking for a job). Now you can make it so only friends can see your profile (and pics). I dont really worry about it. However, like others, I do monitor it to make sure I'm not being tagged in any questionable pics (nor do I put ANY pics up). That way, IF an employer would some how get access to my page the only thing they would see is what kind of music I like, my favorite movies, and that I like to golf. Frankly, if an employer was willing to not hire me over those things I say good riddance.
Edit: I have several friends who just graduated from law school and got jobs with Vault top 20 firms in NYC, and they all have facebook accounts. Judging by what I see on their profiles, they all stuck by these "rules" and it seems to have worked out fine for them.