So. . .whaddya do?

I like people. I like talking to people. I like it when people come and talk to me at the desk. (Also, if I type the word "people" enough times, it starts to look weird to me.) But when friends (or acquaintances) (or people) come up and talk to you at the desk, but they stay too long, what do you do? It's awkward to say, "Hey, sorry, I can't talk to you anymore, I've got to. . .sit here. . .and watch people. . .uh. . .yeah. . ." There's no easy way out. It's just awkward.

I mean, some people just don't get it that we're not here for them to talk to. We have a job to do, people, even if it doesn't look like we're doing anything. So how do you get rid of them nicely? How do you get them to stop leaning on the desk, lingering, blocking the view of other, potentially dangerous people?