It's a great song, and one of the many things I like about it is that it slyly makes reference to its own chord progression -- "I'll take a melody and see what I can do about it / I'll take a simple C to G and feel brand new about it" -- a small testament to Toussaint's cleverness as a songwriter. My discographically sensitive brain is drawing a blank on other song lyrics that refer to their own chords [edit: got one! "Hallelujah" by Leonard Cohen], but it's not exactly a common songwriting device. Given that, it was always a tad disappointing to me that the chords aren't actually C or G: the verse and chorus are an A, D, E. Just now, however, I noticed that the Frankie Miller version has the line: "I'll take a simple D to E and feel brand new about it." Hmm. Given that Garcia was singing the lyric and playing the chords, you would think he'd have noticed. I wonder what was up with that? Maybe his poet's ear was pleased more by the consonance of "see what I can do ... simple C to G" than the clunkier sounding "simple D to E"?
The other slight lyric change that I'd never noticed before was that Garcia sings "I understand why the old fisherman sail along, sail along [etc] / someday he'll be gone," while Miller sings it, "someday you'll be gone." I'm not sure which one I like more, but both are appealingly opaque.