Always managed to avoid it. I do play my squeezebox at pub sessions and occasionally we let the odd one or two to sing but certainly not karaoke style! Something folky with a chorus is good now and then as long as it doesn't get out of hand and they want to sing two in a row!
I'd say evil in a good kind of way. You never know what you might see.... I've found it an interesting experience every time I've been, which is about 3. Now, I would never actually do it myself, but that's because I couldn't carry a tune in a shave mug.
Sometimes your friends surprise you. Went not so long ago with a friend I was visiting and some of his buddies. I knew he could sing, but All Night Long by AC/DC?!? It is impressive to see someone scream in falsetto through a whole song and keep in tune and sounding good.
Sometimes people surprise you in other ways. Seeing one of my professors get drunk and sing Yellow Submarine at a bar in China was a relatively incomparable experience.....
I'm a music teacher, but have seen some folks sing karaoke that was just plain wrong.
I do, however, sing all day long--at school, with the kids, at home, in the car. I think its great for my boys to hear their dad sing and think nothing is weird about that, and I hope that they continue to sing for their whole lives.
But the whole bouncing ball and bad recordings. . .