I'm a big fan of Gmail shortcuts, but they are not very nice with Colemak. If you install Custom keyboard shortcuts through labs, you'll get an extra settings tab to change the defaults. I thought I'd share my minimalist change:
Back to threadlist : change from u to h
Newer conversation : change from k to u
Older conversation : change from j to e
Previous message : change from p to n
Next message : change from n to i
Archive : change from e to E
Archive and go to the previous conversation : add alternative ,