I've got a Garmin Forerunner 301 that I use for running/biking/car trips. It sometimes takes a long time to pick up a signal which is kind of annoying, but otherwise seems to be a nice little unit with built-in heart-rate monitoring and the like. I wanted to use it on Linux as I don't use Windows. A quick search revealed this entry which gives a couple of command lines to grab data off the GPS. After a quick apt-get install, I tried them and they seem to work. The first just gives a long series of coordinates. The second gives a .kml file which I was able to import into Google Earth (though that's extremely slow on my hardware, so not very useful to me).
gpsbabel -t -i garmin -f /dev/ttyUSB0 -o gpsdrive -F tracks.gps gpsbabel -t -i garmin -f /dev/ttyUSB0 -o kml,points=0,line_color=ff0000ff -F waypoints.kml
I'd really like to put some data into Open Street Map. It would be a fun project for the summer to bike around the neighbourhood and fill out their data.