<p>I've always been intrigued by Map Routing, but I've never found any good introductory (or even advanced!) level tutorials on it. Does anybody have any pointers, hints, etc?</p>

<p><strong>Update:</strong> I'm primarily looking for pointers as to how a map system is implemented (data structures, algorithms, etc).</p>

Take a look at the
open street map project
to see how this sort of thing is being tackled in a truely free software project using only user supplied and licensed data and have a
wiki containing stuff you might find interesting
.
A few years back the guys involved where pretty easy going and answered lots of questions I had so I see no reason why they still aren't a nice bunch.