I dont wear any pants more than a couple days in a row, but between washes/dry cleanings, I'd say 15+. For dress pants, maybe I'll iron them once in between, but I'm not doing anything that's going to make these things dirty faster than that. Frequent dry cleaning wears them out, too.
Now, if they smell, I'm obviously not going to keep wearing them. But I'm not playing basketball in them, I'm sitting at my desk doing my job. For jeans, if airing them out a bit to get the beer/cigarette smell out after a night at the bar doesn't do it, they go right into the wash. But I don't get to do that as much anymore, so its less of an issue. (No, I don't smoke, but in VA ppl can still smoke in bars, it sticks to you).