I did this as bit of fun last night. I asked the bar staff if they would like the tip in mBTC. Within a few minutes there was a group of five or so people learning about bitcoins. One of the bar tenders had a samsung, the other an iphone. I downloaded mycelium on to the samsung and sent her the tip and then she split it with the other bar tender by sending to some iphone app I had never heard of. People were suitably impressed and it's probably not a bad way to spread the message. It didn't hurt that during the discussion the price rose a few points.