I think Earth Wind and Fire are an old disco band who sang a classic called "Boogie Wonderland" ^__^

As for Avril doing "Knocking on Heaven's Door"... just take solace in the fact you've never heard her cover of System of a Down's "Chop Suey"... *shudders*

oooh also looking forward to hearing Skin's collaboration (if it's the same Skin I'm thinking off) and I've heard Cheb Ami sing before on one of Sting's tracks... some really cool arabic wailing