I always liked that Led Zep track and especially the bass part. That's where a lot of the fun comes from.
The whole idea of a "mash-up" interests me. Where does one draw the line?
The Beatles did it! Geoff Emerick reveals this in his book
Here, There and Everywhere. They wanted an interlude in one song ("Being For The Benefit of Mr Kite" IIRC) but George Martin didn't want to pay (and have to explain to accountants) so they took a track from an EMI library disc, transferred it to tape, cut the tape up into segments, threw the segments up in the air and re-assembled them in the sequence they landed in. Now it wasn't that other composition with all the rights attached to it.
The basic idea of using bits and pieces of other and not your own recordings goes back to the 50s at least. See
http://en.wikipedia.org/wiki/Mashup_(music).
So it may get to be a matter of exactly where the line is drawn. That Wikipedia article uses the word "purloined". Well, David Byrne and Brian Eno made a record (
My Life In The Bush Of Ghosts) using what they called "found" sounds. These were mostly from radio broadcasts and they were used as the vocals and backing tracks were recorded for them.
I think we get a lot more of it today because it's so much easier to do with the technology we have. Byrne and Eno had a heck of a time making loops of their "found" vocals, then getting them to run in time with each other and with the backing track - and when I say "loops" they had to make physical loops of actual tape. These days this sort of thing is much easier to do.
