At the time I was a poor grad student and was shopping for a portable AC unit to survive the summer in my sweltering apartment. There were about 5 craigslist sites within driving distance, and I was checking all of them, since saving 20 bucks was easily worth an extra hour of driving at that point. :) Figured a simple thing to learn some basics would be a page that would just spit out the links to multiple craigslist results pages matching a given search.
I literally went to the library and got a book called something like, "Basic web development using PHP and MySQL". The initial site was... very basic. Before I made it I'd looked around for existing solutions, and so when it was done I replied to the few forum threads I'd found, where people were looking for the same thing. It basically grew organically from there. (And over time I made it somewhat less basic. Although the design is looking pretty dated at this point; we're currently working hard on a long-overdue responsive redesign.)
A couple years later I made (an early version of) http://www.autotempest.com, which is like kayak.com for used cars. Then around 2009 I quit my day job and hired my first employee. Have been doing this ever since.
Anyways, keep up the awesome work, and I'm glad it has all worked out for you!
Any way I can get this half decade long question answered? :)