I once used my car's Tom Tom GPS with my bike (before I found out it had a bicycling feature) and I found it useful but I was nervous about killing the battery with an all day ride. so I only used it in conjunction with maps and only when I needed to verify where I was. so, of and on and off and on. PIA ... for a while I rode with it on and it was fun listening to verbal queues just like in my car. so it was perfectly adequate helping me rack up big miles on an all-day ride. now that I know it has a cycling mode - I may be safer using it next time. I should figure out a better way to mount/carry it though. it was in my rear rack trunk but I got tired of in and outs of that methods so I used the top bungees of the trunk bag and just kept it tied to the top outside of the bag. mounting it somehow on the bars would be better.

I think a bicycling specific GPS would be marvelous!