In the old, pre-garmin days, I was a pretty good judge of pace. Since getting my first garmin in 1999, I found myself obsessing for a few years. I've gone back to running by perceived effort and my times are almost back to where they were a decade ago. (Probably coincidence).
I still wear the garmin though so I can geek out when I get home. If I'm racing well, I don't have time to look at it, if I'm not running well I might sneak a peak to try to maintain pace. I never set a beep though, I think that is bad manners in races, although fine in training. As for those who have beeping garmins but are listening to their ipods - don't take me there!
A couple of years ago I ran an off-road race where watches and garmins were banned. All runners were aked to predict their finish time. I finished 8 seconds faster than I had predicted and won a bottle of fizz for being the closest to my time. Once you know your body You don't really need the technology!