"John, I'm really curious:
What do you do for work that allows you to constantly quit and be rehired and that pays well enough to cover the costs of thru-hiking and several months of mortgage payments?"
Different things over time. I worked as a paralegal between the AT and PCT, and generally in the ski industry (summers off, fall rehire) until 2005. Before the CDT, I worked at Best Buy (a disposable job if I ever had one), and currently I am a database analyst. After the PCT this year, we will probably both return to her outdoor retail gig, and get laid off just in time for the AT 2011.
Since the CDT, I have been attempting to make a career change into national security, my area of study and interest. I would finally be willing to give up the thru-hike/travel/ski lifestyle to do it. Some (but unexpectedly, certainly not all) potential employers in this area have viewed my background negatively.
ETA: As far as $$$, the best years of my life have been the ones where I earned like $4000. When not on the trail, I just don't spend much. No cell, no TV, no cable, '89 Corolla, one modest Kona bike, hardly drink, mostly vegetarian, etc. We are currently refi-ing from a 15yr fixed into a 30yr fixed, which will cut our monthly payment almost in half and enable us to get by with simpler jobs and longer trips.