Been a police/fire/EMS dispatcher for four-plus years in two small towns, one of them full time. Here's my take:
I always assume that dozens of people are listening on their scanners. I have to assume this, because generally there are (unless I got screwed and am working the overnight shift). Everyone in small towns are nosy, and hyperprotective about their property. I can't tell you how many times I've received calls from "concerned local citizens" (bonus points to anyone who gets the reference

).
Generally I thank the caller, take the information they have, and their name and callback number. I'd rather make someone feel appreciated, so that they call when they see something next time (not to mention so that they're more inclined to vote in favor of us when the town meetings come around) than alienate them and kill off an information source. Granted, not everyone in my department is like this, but I'd say the majority are.
Now, a few things to keep in mind:
1. If you're calling a small town, understand that most of them only have one dispatcher on at any given point. This is how it is at my department. Thus, when something goes down, the dispatcher is busting his or her ass getting everything done, they're under stress, and they're alone. This may precipitate some measure of frustration or impatience when their attention is divided into a fourth, fifth, or sixth direction.
2. If you're calling a city department, understand that they never hire enough dispatchers, and it's stress from the get-go. This generally causes 'em to be very blunt and jaded, among other things.
Of course, there are bad dispatchers out there. Bad eggs in every profession. But I honestly feel that people don't usually understand the dynamics involved, especially in small-town dispatching, when they get upset over anything other than stellar, velvet-glove treatment from the department.