If you ride in the back country or hike with a GPS receiver, this may be of interest.
I made some test tracks in really wet woods to gather evidence under controlled conditions on the perennial topic of tracks under tree cover. The results are not surprising. The executive summary:
1) Typical consumer GPS receivers can record useful tracks under heavy, wet foliage when reception is not obstructed by the user.
2) Forget about carrying the antenna on your body in the forest. Hand-hold it or use an amplified antenna on your hat.http://users.adelphia.net/~fhiltz/TrailTrack.zip
(13KB) includes three files. TrailTrack.mps and TrailTrack.gpx contain the tracks in Garmin and GPX formats. TrailTrack.txt is a more detailed report.