I think a greeting while responding is nice (as Diana puts it… organic), but a greeting alone I find to be a bit weird. It’s like that greeter at the door of the hardware store, they always make me feel weird! But then, I prefer to shop without disruption, and the idea of a store person approaching me to see if I need help creeps me out… I prefer it more if there is someone just there somewhere, that I can ask for help if I need it!
But that said, if someone is particluarly sociable and wants to personally greet new or returning users, I’m all for them being “allowed” to do that!