Echoing some of the previous posts, GDAE is probably better for playing the tunes (i.e. melody) than GDAD. GDAD is great (in my experience) for accompaniment.

I know someone who used to play GDAD, and would capo up at the seventh fret when he wanted to play melody. The capoed (sp?) instrument would then be DAEA, so the bottom three pairs may be played as the top three pairs on an uncapoed GDAE instrument. I myself do not like this approach, because I find the frets to be too close together up there. But mandolin players would probably feel right at home!

Don