Recovering at the office from a weekend at Wheatland (in Michigan). Yegodsandlittlefishes am I knackered.
We (my band and I) try and measure the audience response/participation and use THAT as a guide to what may be "nagging" to some people. If the crac is good and we've got them wrapped around our little finger musically - and they like the music and what not, then a little playfullness once in a while makes it a bit more fun for us (as players) and them as participants. Encouraging people who are singing along on their own is one thing - rather like giving permission to sing LOUDER - forcing the issue is exactly that.
If you're playing a place that you've never played before, or bands of your type rarely play, sometimes subtle (or not so subtle) cues are appreciated, no?
I remember one small town we played at this summer where we stole a Fionna Ritchie line and "defy'd them to keep their feet still." We finished the first part of the first reel and there were a dozen people dancing - finished the set of reels and there wasn't room to move for all the people up - never mind we'd played plenty of tunes before that, we just told them it was ok to react to what was going on.
Back to my nap... ummmm... work.