Duane Allman and Clapton both play on the Layla track, Clapton said the song was still in a very basic form when they started the recording session, that Duane added a bunch of riffs to the song and really brought it to life, the keyboard player came up with the long outro piece and Allman and Clapton both are playing slide over that, Clapton is in background if you listen to it closely, Layla was a great album, I think because it was a great collaboration of great players. Guitar Player magazine did some good fearture articles on Allman and Clapton where they both gave the layout of what went on during the Layla session, alot of stuff never made it on the album, if you ever see an old record called Duane Allman Anthology, there's a great version of "Mean Old World" by DA&EC on Dobro's