As mentioned at the top of the content on the home page, we run Linux on our computers. Some may think that it could be a hinderance to task a, b, or c, but it's almost never the case these days, as long as you're willing to read a little, and tell others when their software doesn't support you.
The first step in making your life easier as a linux-based geocacher is to get things setup so when you are looking at a cache on geocaching.com and you want to get the cache imported in to your GPS unit as a waypoint, you should be able to just click the "LOC Waypoint File" button and be done with it.
This takes a couple of steps to setup on your system... it basically boils down to 1) installing gpsbabel on your system, and then 2) getting your web browser to understand how to deal with those LOC waypoint files.
First things first, install GPSBabel. Whatever Linux distribution you're running, there should be an easy way to install it on to your system. Check your distributions software management system - it should be there.
Next, you need to install the mime type on to your system or your web browser so that your browser understands what to do with those LOC waypoint files. I happen to run KDE and use Konqueror as my primary web browser, so I'll give the example that I used myself - your results will vary, but there will be heaps of information elsewhere on how to install new mime types in to your browser, whether it be Firefox, Opera, or even Links, if you're so inclined.
So, in KDE's Konqueror web browser, open up "Configure
Konqueror" under the Settings menu, and then click on the "File Associations" icon on the left side. The right side should now say "Configure file associations". Click "Add" at the bottom of that list and you should get a new dialog window popping up, "Create New File Type". Select the application group, and for the type name, enter "xml-loc" and hit OK.
Now you should be looking at the "Configure file associations" window again with your newly
created entry highlighted. We need to now associate this mime type with filename patterns, and configure an application to run. On the right, underneath "Filename patterns", click Add, and enter "*.loc", then OK. Under "Application Preference Order" in the lower right, click Add, and in the list of applications that comes up, enter in a name such as "gpsbabel", as seen here on the right:
Now in the "Application Preference Order" box you'll see what you've entered. Click on it and then click Edit. In the new window that opens, click on the Application tab. You'll need to enter the command line for gpsbabel as I've done in this example window... please note that these settings
work for my GPS, a Garmin GPSMap 60CSX, your command line may (and probably will) be different - please check the gpsbabel website and test from the command line yourself.
Down below in the "Supported file types:" section, click Add and then use your newly created Application -> xml-loc mime type. Click Add, and then back on the "Properties for gpsbabel.desktop" window, click OK, as you should now be done.
Click OK on the main "Configure - Konqueror", and all going well, you should be done.

Next time you click on the "LOC Waypoint File" button on a cache listing page, you should see a pop-up dialog similar to the following:
Enjoy!