NPCs in your campaign: do you use many?

[Boccaccio Barbarossa]

To BBarbarosa: I know my players well too, but they play a variety of roles. The lawful neutral cleric will hang with different people than the chaotic neutral barbarian or the chaotic evil ranger or the neutral good scholary wizard... That's good IMO, since when my players experience different "personalities" they get to see the differences in social life that come along.

To BAlex: A good reward for me is that sometimes the PCs return to a city or village just to check on the NPCs friends.

I definitely agree - there is a lot of "down time" when parties are split. I shouldn't say down time because that is often when the greatest role-playing occurs, but essentially, we all undertsnad that, like you pointed out, the conniving Borcan aristocrat just doesn't hang out with the same types of people as the pious cleric of the Morninglord. So it is definitely important to accomodate the varying tastes.

Second point: that's a great thing, too: when PCs take a detour just to visit certain NPCs. (Although, in our game, it has tended to happen quite a bit to one particular retired adventurer who now concentrates on helping other heors and running his vineyard, about an hour';s ride outside karina... )

[tec-goblin]

Well, it always depend on the size and type of campaign. In my average 2-year campaign there are just hundreds of NPCs. They meet one new in each session. But the number of 10 "regulars" isn't crazy - just keep in mind that the synthesis of these 10 can actually change in the course of a long campaign. Of course in these numbers, I count all well developped villains.
I am playing a political campaign right now - where everything is about NPCs (there are no "monsters" in the traditional sense).
I have a huge drawing with 45 persons and 80 arrows and a nice list with short stats, description, allegiances and hooks for EVERYONE. But there are around 10 who are more important than the rest.

Players tend to keep notes or keep logs to remember what's happening (we play by msn). Forgetting the name of a single NPC who might help you might prove a blatant faux-pas in French/Montaigne court.