Interesting thread, particularly the bit about whether you should or should not use a finger across two strings.

I'm not a fiddler, just a guitarist, and I originally taught myself to play by ear, with no books or anything (at least, I worked out a few basic chords etc. on my own). Then later on, I bought a "teach yourself guitar" book, and one of the things it said was that using the thumb to hold down the 6th string (as I often did, e.g. in the D chord) was a no-no. By then I'd got into the habit of doing it, and I couldn't get out of it, and I worried about this for a while. But then I saw Eric Clapton live, and noticed he was using his thumb to hold down the 6th string - I figured if it was good enough for him...!

I sometimes wonder if these "rules" about what you should and shouldn't do can do more harm than good, and hamper creativity - what do others think?