N810 using maemo-mapper for recording mountain biking trips works quite well. I put the N810 in it's standard pouch, then inside an Aquapac with a sheet of foam for protection. Turn on at the car, check it's got a lock and is recording the track, then pack it inside the Camelbak and forget it's there, export GPX files once you're home and view routes in something like SportTracks.

Maemo-Mapper with the standard maps + google maps and google satellite imagery) works quite well. You can pre-cache the area you are going to, so you have a bit more than just track recording should you need it. I did find this useful when travelling abroad and also when trying to find our original track whilst out biking, to confirm current location relative to the rest of the route.

It's not quite as slick as a Garmin Edge or other outdoor specific GPSes, but if you just use it occasionally and don't want to spend twice as much, the Nokia works pretty well.