Totally agree w/DH. We initially started w/the friends page as that was all that was available. It was a major hassle and everytime FB did an update, you lost them and had to start all over.
We switched to "like" and do no more than once p/week. I think anymore than that is when peeps get rid of it as spam. Oh, and always offering something beneficial to the client keeps them interested in and constantly growing.