*TECHNICAL UPDATE:*

I just tested a working solution on Windows using the Quantum GIS freeware,
which also works on Linux and on the Mac, so I'm sure it's a cross-platform
solution that everyone can benefit from.

How to view & edit tracks on USGS WMS databases using QGIS freeeware
https://groups.google.com/d/msg/alt.comp.freeware/IeNTm2cOrd8/F_ftT-p5CAAJ

In addition, for cross-platform mobile devices, this solution works:

How to record tracks on USGS geocalibrated PDFs using Avenza freeware
https://groups.google.com/forum/#!topic/comp.mobile.android/zNKD3jyeye4

How to record GPX tracks on iOS & Android freeware & copy to the desktop
https://groups.google.com/d/msg/comp.mobile.android/zNKD3jyeye4/vxLvk87oAgAJ

This solution, unfortunately, only works on Windows at this time!

How to freely geocalibrate multiple USGS quadrangles into a single PDF map
https://groups.google.com/d/msg/alt.comp.freeware/W3IjaKFeLrM/TpFbNWiIAAAJ

What's missing, I think, are the following missing Windows/Linux solutions:
a. How to use the Quantum GIS USGS WMS method wholly offline (if possible)
b. How to combine & geoCalibrate USGS geoPDF quadrangles using Quantum GIS

The reason that (a) is needed is because it's a bad idea to be required to
use the Internet for personal private mapping solutions, while the reason
for (b) is that the Avenza solution on the mobile device sucks when your
hike crosses USGS quadrangle borders (which it often will do) so you need
to be able to combine geocalibrated PDFs on the Windows or Linux desktop.

(The current free solution for combining geoPDFs only works on Windows.)