I have a friend who regularly pulls her credit report to make sure nothing has gone awry. I thought it wouldn't be a bad thing to do, but didn't want to spend any money doing it. I have pretty good credit so I wasn't too worried.
Yesterday, I read about annualcreditreport.com at beingfrugal.net. This site lets you obtain your credit report for free once a year from 3 different reporting agencies: Equifax, Experian and TransUnion. According to the FAQ, you can space out your requests. Yesterday, I got mine from Equifax. Disappointingly, it did not have my credit score (which apparently is never free to obtain), but the rest of the information was useful. At 17 pages long, there's a lot of stuff there - student loans, credit cards, closed accounts, soft and hard inquiries on your credit, negatives (I don't have any - woo hoo!), etc. It also reminds you that it's a good idea to keep your oldest line of credit open. Don't close that first credit card or bank account if you can help it.
While opening a new credit card account has an effect on your account, checking your own credit does not. There are soft inquiries and hard inquiries, and this is a soft one (see here for more info).
Going along with the credit thing, I called 1-888-5-OPT-OUT yesterday so that I would stop getting offers from credit card and insurance companies in the mail. It is super easy and completely automated. It does ask for your SSN, and I hate to give that out, but I have read about enough people taking advantage of this that I'm not too worried.