I am a proud owner of an Garmin etrex 30. Since I do run Linux on all my machines at home, I tried several ways to update the firmware of this device. Unfortunately this is not possible, using WebUpdater from garmin directly. A tool which should make it easy (and most probably it does on windows and/or mac) makes it hard to do on Linux.
Anyways, a download of the lates firmware can be found at http://garmin-etrex.wikispaces.com/firmware. You just need to rename the Downloaded file to GUPDATE.GCD and move it to /Garmin/ on your Garmin device.
After a restart of the eTrex 30, all seems to be fine.