I'm all for playlists...
If i read one, and know every track on there (and a lot of it's not to my taste), then I know it's a venue I'm going to swerve.
If I don't know a fair amount of what's played but like the ones I do know on the list, then it's more likely to encourage me off my sofa (which not a lot is at the minute for various reasons).
If you are scared that someone is going to copy all of your best plays (max 22 per hour spot?) then your playbox isn't strong enough. For every record you play you should have another 4 of equal merit in a 100 count box - otherwise IMO you are just playing at it.