I could have used this when I was researching trails for Footprint Press guidebooks:
Trackstick II Personal GPS Tracker
Tracksticks are tiny GPS location recorders capable of continuously logging their own location histories for extended periods of time. The Trackstick records its own location, time, date, speed, heading and altitude at preset intervals. Traveled routes can be viewed directly in Google Earth TM . Includes GPX photo stamping feature for adding your favorite photos to your own maps., $149.00 Click here for details.
Like many innovations, this could be used for good or evil. Personnally, I view it as another potential tool against my privacy, of which I have very little left. On the positive side, looks handy to me,