I'm just about finished for my first mileage run ... it was certainly an experience and I've learned lots about traveling (or rather, what to do when it goes wrong).
I'm in the final few segments of this beast:
LHR-DUB-PHL-DCA-ORD-IAH-DEN-COS-DEN-IAH-ORD-PVD-IAD-SFO-PHX-SNA-SFO-SMF-ORD-DCA-PHL-DUB-BRS
(Obviously not all on one ticket - people might recognize the locations which have been cheap over the last few months ... PVD, SNA etc ... and the final segment is with the luxury Ryanair, so no miles there). It all came out at under 2c/mile and should net me around 21,000 miles.
I reckon it'll be a few months before I try something like this again!