Currently there is no linux support from Garmin. To be able to use paperless geocaching under Linux I wrote a Browser plugin that simulates the Garmin Communicator Plugin. Using this plugin your are able to transfer Geocaches from Geocaching.com using the "Send to Gps" button.
I've been recently thinking about if my next computer should be a Mac or a Linux box since while my MacBook Pro is miraculously still working, I'm expecting that it's going to kick the bucket sooner rather than later. The Garmin Plugin was one of the things that I figured I'd miss if I decided to go with the Linux option, since it makes posting to Daily Mile really easy. On a whim, I searched for a Linux version of the Garmin Plugin, and to my surprise, I found it. It hasn't been tested with Daily Mile, but if it doesn't work, I don't expect it to be that hard to fix it.