You wouldn't leave the door to your house unlocked at night in the hopes that you'll catch a thief red-handed, would you? Then why wait until thieves open credit accounts in your name before being notified that there's a problem.
Up until recently I was a big proponent of Equifax's Credit Watch service, whereby an email notification is received whenever a change occurs to your credit report. You then have to sift through the changes and make sure nothing fraudulent has occurred. Sounds a little too late to me, after all if something has happened and somebody has managed to steal your identity and open credit in your name, the damage is already done and you're left a mess to clean up.