Me and a friend of mine is thinking of starting a guitar duo, and regarding that i was wondering if anyone has any tips concering this. What can be done with a duo? What makes a duo with two guitars differ from one? What opportunities are there purely musical wise?
look at the Singers/songwriters of the 60's 70's
and modern things like G. Love and Special Sauce
or take things like Jack Johnson, and double the awesome because there's two of you rather than just one.
thats assuming you have creativity, and good musical taste.
or look at the Jack Johnson and G Love colabs.

or Dave Matthews and Tim Reynolds

or any band that does acoustic versions of their songs.
look at flight of the concords
i think duos are awesome
one can sing and play chords while th other plays a lead
ive written a couple duets with guitars
both of you sing and play
one can play the bass instead of guitar or piano
really it just matters how musically talented you are