Somewhere around 100 hours, for three playthroughs, each one has been taken through all the DLCs, neutral, evil, good, all that jazz.
I also agree with BN, there's little variety between different karmic paths, and once Broken Steel came around it can't even be considered a shadow of a RPG.
Played to keep up with the Fallout lore, there's probably way more hours unrecorded because I would save then play around five hours using only autosave in order to finish certain quests, I didn't want to max out my characters before I got at least three quarters through.