Interview with Opeth in ARTISTdirect... 27 May 2008

Interesting. The comment about the exorcist artwork similarities is pretty neat http://i103.photobucket.com/albums/m142/rockyroadz/MySpaceBio/TheExorcistMoviePoster-1.jpg.

Also Mike mentioned Led Zeppelin as an influence, specifically the song Friends. I just listened to it and wow, especially the synth stuff going on is VERY similar to Watershed. Pretty sweet if you ask me. I love that Mike has never been afraid to admit his influences, in fact he thrives on it.
 
you're right heir apparent, i found a huge resemblance between friends and atonement, i think it was that song (well... and many songs of opeth In GoR and WS), especially due to the mellotron...