I know what you mean, most of the time you don't need a wrist map. Having said that, I can definitely see some good uses for it. There are a number of times where I've been lost on ultra-marathons as a result of missing a signpost, and have also managed to get lost on long bike rides in unfamiliar areas. I like the idea of being able to upload a gpx file to your wristwatch before an ultra or long ride, so that you can make sure you don't go too far off course. Whilst a phone with mapping is really useful, it's not always practical, especially from a battery life perspective over longer runs / rides.
Perhaps I just love maps a little too much. I have a geography degree and also a masters in geographic information systems. I get quite excited about the use of mapping technology and the potential for location based services etc.
I like the look of the Pebble, very cool. Now if they could only make a lightweight GPS enabled mobile phone with a decent battery life to communicate with it