Even if my mouth is full, I try to smile, and at least nod to show my appreciation for good service. I always thank the server whenever they bring something to the table, and when asking for something, I usually say something along the lines of, “When you get a chance, could you possibly bring some sugar? Thanks!” If they forget, I’ll just ask again, because, hey, they have a lot they have to remember, especially in those places which (inexplicably) don’t use order pads.
I figure servers get a lot of abuse from rude customers, and perhaps by being extra-nice, I can brighten their day just a bit. It also has the added benefit of getting me great service.
When the service has been especially good, I’ll usually speak to the manager on the way out, and let them know, or fill out a comment card if one is available. (I’ve never complained about a server, because I figure they’ve probably had a rotten day.) My husband and I are very good tippers, and pleasantly enough, we’re remembered at all of the establishments we dine, and the staff is especially good to us.