It happens to everyone, no matter where you play; some idiot is bound to come up to you and ask if you do Stairway to Heaven, or Smoke on the Water. The best response, I find (aside from stoically ignoring them), is to actually start playing it. It’s also fun to play during a quiet period in a Celtic jam, and see if anyone notices.
Would be cooler without the annoying intro and the way the TV news guy cuts Anne off before she’s properly finished.
Here’s another sweet Celtic tribute to Zeppelin, with crop circles: http://www.youtube.com/watch?v=GQ_q_ORctQk&NR=1