Thankfulness and Appreciation

I'm struggling today with wanting to use positive reenforcement and letting people know that I really appreciate what they do, and wondering if I should stop thanking people for doing things that are actually their jobs, and they get paid for them. The problem with thanking people too often, I think, is that they start to think that what they are doing is a favor to you instead of an integral part of keeping the business running. Therefore, they stop doing those items that they don't really like to do unless they are specifically asked, and things don't get done in a timely manner. And besides, who wants to constantly remind someone to do their job?