I use the Cities section far more than the others, followed by the section on People, both in prep and at the table. Wilderness and Dungeon do get use as well, but not as often.
I don't really use the stats, though, mainly because they are 3.0, and I was running 3.5 and am now running a house-ruled version of Pathfinder. The encounter tables for people (as opposed to monsters) however, have seen use as they are good inspiration anyway. The Mother of All Encounter Tables has since covered that ground fairly well, I think, so if you were to do a similar product again, it might be a good idea to make sure any encounter charts really stand out from more generic lists.
A set of stats for all the members of a city watch, temple, magical academy, merchant caravan, thieves' guild etc would be useful, for example - stock fantasy elements that are a real pain to draw up for DMs, yet are more than just simple lists of encounters by CR. The DMG II had some cool stat blocks in this vein, but there is plenty of room to develop the concept into plug-and-play collections that can slot right into a campaign.