I love Little Martha too! Great tune. I first heard it in Leo Kottke's Home & Away video. Then I bought Eat a Peach!! Love the Allman Bros. I do Big Yellow Taxi as well but in Open D it's either too high or too low for me. I like it in open G. Open D is good blues to be sure and maybe the Black Crowes, She Talks to Angels? What I love about open D is that when you bring the F# back up to G, you get DADGAD...Love alternate tunings in general.
Here's my Little Martha:
http://ca.youtube.com/watch?v=KSouq4...e=channel_page