I'm a long time Linux user, but noob on the geocaching front. My impatience pushed me into buying a Magellan Triton 300 at a local sporting goods store before I had a chance to read up on it. Once I got home, it didn't take long to discover some of it's issues, namely lack of non Windows support.
But...
In the week that I have had it now, I have found (on tritonforum.com) how to switch the unit into diagnostic mode so that it shows up as a usb drive, and last night discovered which file holds the geocache, waypoint, route, etc data. It is an sqlite3 file, and with a little more work on my part, I should be able to crack it down further. Since it is an SQL database, I have a feeling that the unit in normal pc connection mode is acting as a sudo network interface instead of a storage device.
With this knowledge, I hope to have something cobbled together before the end of July as I will be on vacation in Idaho then, and am going to Dublin, Ireland the first week of August. I plan on geocaching both weeks, and want to at least preload some cache sites for each area. I'll post a new thread once I have more progress to report.