Should employees be allowed to look at facebook, twitter, etc?

[Rita]

I was talking in my business class about companies looking at your facebook and twitter to see who they really are hiring. Personally, I don't think its a big deal especially if you don't put anything too extreme or that if you do you know how to use privacy settings. But my problem would be if they asked for my username and password, where it crosses the line such as my personal messages. Granted my post are public, but messages are where I vent to my best friend or if I'm going through a divorce or medical problem that I'm talking to a friend about, things I don't think are needed information that my boss needs to know. I compare this to my boss asking to see my text messages which are also (in some case) just as easy to see with a username and password online also. I wanted to see what other people think about this issue with hiring..so what do you think???