Prize for nice customers?

Just catching up on my blog reading, and noticed this post on Seth's Blog.

We could do that, offer a prize to the nicest customer who called each day. Decide by a quick straw poll at the end of the day, and send them a small prize. There might not be someone outstandingly super-nice every day, but often there is, and we do talk about it, but we would never actually tell them "hey, you're such a pleasure to deal with, we really appreciate your custom", but why shouldn't we? I'd love it if I was that customer.

And, of course, it's great for word-of-mouth marketing:

"Where did you get those lovely flowers?"
"Oh, 0800handyman sent them to me because I am really nice"