It varies for everybody. I only use it for tile and grout targeted to communities that I know will be having gout issues. I am mostly looking for repairs. I can send out a small mailing and get 1 $650 regrout so it's pretty good for me. Never really used it for carpet cleaning but quite a few guys here have.
I spend about $160 month, Specials like 1 room free with the purchase of 3 or more, Free deodorizer, free Kitchen Tile floor which leads to refferals and call backs in less than 4 months. I find that the key is to be unique in your area, see what others are offering and do something different that gets people attention. I also give 30 days guarantee, folks like that since they may have never heard of you, it gives them peace of mind.