It's an awesome visualisation tool for GPS routes. As long as you're using software (I've been using GPS Trackmaker under Windows) that can export to .kml/.kmz format, you're set.
No worries. What I've learned over the past few years is that the important thing is for your GPS software to be able to export to a file format that everyone else can read. This typically means .loc, .gps, and .kml/.kmz as a baseline - pretty much any GPS software worth its salt will be able to handle at least two of those three formats, and Google Earth can handle them all though it only lets you save as .kml/.kmz.
I've been using .kml/.kmz for the last year-and-a-bit or so for geocaching simply because Google Earth is free, runs on every major platform, and as a result is the most easily-distributed format - but I can still import .loc or .gps data from the software I use to edit the routes, etc. into Google Earth for visualisation. Seems to work out pretty well.