There are a lot of free web services and I use a very small hand full of them. I also run one of those free services and am truly thankful for every individual using my service.
Craigslist, a free service with so many users they probably should care less if I use it...tells me they really appreciate it every time I post something there. Just like the lady selling corn at the street fair.
How often do YOU tell your users/customers that you really appreciate them?