Retail managers and supervisors - effect of consumer input on workers?

[Foogoo]

To anyone who's ever been a retail or otherwise customer service establishment manager or supervisor: what effect does positive customer input regarding their experience with a worker or salesperson have on the person in question?

Especially if I have a better-than-expected experience with a plain salesperson or retailer, I sometimes write a letter to the manager regarding my positive experience since I figure it's the least I can do for someone who put forth the extra effort.

At a bank I worked briefly at, I believe we got personalized "baseball cards" after two positive customer references...