I was up in NYC at the end of June and caught two celebrity-filled Broadway shows: Hedwig and the Angry Inch and the Cripple of Inishmaan.
Hedwig was easily the most fun I've ever had a musical (technically a rock opera). Neil Patrick Harris was superb. Hedwig's backing band also was fantastic in a rock and roll way, not a 'talented Broadway musician' type way. This made a lot more sense once I read their bios: they include former members of the Antlers, the Wallflowers, and Morningwood. Even the understudy for Hedwig's love Yitzhak is the lead singer of popular Led Zeppelin tribute band Lez Zeppelin (they play the State Theatre all the time but I've never seen them).
Daniel Radcliffe, aka Harry Potter, starred in the Cripple of Inishmaan, a dark comedy by my favorite playright Martin McDonough (The Pillowman being my favorite of his work, though I've never seen anything by him that wasn't awesome. Radcliffe was great, but was easily the sixth or seventh best actor in the play -- that's how good everyone else was.
I remember reading an article in college that said the Beatles' "Yesterday" was the most covered song of all time. Who knows if that is true (then or now). But even if it is, it certainly doesn't mean that it's the most common cover song experienced by any one individual. I've never heard a band cover that song in concert. The only time I've heard anyone sing it was the middle-aged Asian street busker who played acoustic songs at the South Kensington tube stop when I lived in London (he knew neither the correct music or lyrics to the song, which somehow made it more endearing when I'd hear it nearly every day on the way home from school).
In thinking through the most common cover songs in my musical experience (and I'm setting aside cover bands), the most common cover I've heard live has to be the Stooges' "I Wanna Be Your Dog." I mean two bands on the second Weezer Cruise alone covered it, for goodness sake (The Orwells and Cat Power). I've seen people from Joan Jett to Jack White cover it. No other song is even close in my personal experience. How about you?