Yeh I was testing out a 7-string guitar the other week, trying to decide if I would get anything out of having one, as compared to another 6-string. The guy who was showing me had a couple of 7-strings himself and was explaining why the other string is there and what you can use it for. Then I made a comment about using my thumb to fret slash-chords, and he goes, "Ahhh.. so you like to play more jazzy stuff" or something along those lines. I decided that the 7-string guitar is not for me at stage.. may be later on.

I love using my thumb for that kind of thing.. Using my thumb came naturally to me. I always knew that I was supposedly not meant to be using the thumb like that but then I wasn't playing classical guitar so it didn't bother me that much. I've seen many other great guitarists use their thumb this way and I have instructed other people to use it for various chords that are otherwise hard to do.. such as the D/F# chord which Pink Floyd uses in their Wish You Were Here song. Having come up with a new chord for myself recently, I think Chris Schelgel (sorry Chris, I can't spell your name :)) labelled it the D9/F# chord or something, I can now more easily see how to fret a D/F# chord without the thumb but it doesn't sound anything like the chord used in the Pink Floyd song unless I use my thumb.