The only time I use my GPS is on the boat, hiking and hunting. There are no road signs on the ocean or in the woods. As far as using one on the bike I think they're more of a distraction than anything. I've brought it on the bike and never looked at it because I usually plan my route ahead of time. Not only that, most of the GPS units that would mount on a bike have small screens that make them tough to see. I have a handlebar mount for my Magellan Meridian and it's tough to see unless I stop and look closely at the screen. Actually the feature I used most was my speed and compass setting which is easier to see than the road map lines. My speedo is pretty accurate until I hit around 40 MPH then error starts increasing. At 65 my speedo is off +6 MPH.
My advice is to buy a good map or keep the GPS in the saddlebag as a backup. You may only need it occasionally when you get turned around and can't find a road sign or crossroad. I've had great luck with my Magellan Meridian but I know Garmin makes a first rate product as well.
