As to Joel’s comment, I’m pretty sure every joke has basically been done. At least we know he reads XKCD. I mean there are like 40K webcomics out there, some of them have been running for years and years. And then there’s every movie, TV show, comic book, strip and stand up routine. Of course, the context of a joke matters. Given a particular situation or characters, the same joke could be more or less funny. The “why did the chicken cross the road” joke in Alien Nation (the movie) was actually funny, at least compared to how non-funny that joke usually is. The thing is, you can’t just watch a clip, it takes half the movie to set it up for it to even be as modestly amusing as it is.
I’m actually surprised there are any new songs these days. It seems like every combination of notes and instruments would have been tried by now. Maybe this (youtube) lends some credence to the idea that we’re approaching a media singularity, where the answer to every sentence beginning with “hey have you heard…” is “Yes.”