I would think this would be an UNLIKELY partnership, for some reason these two conferences just don't have much in common.
Actually it works quite well, but both conferences would need to coordinate scheduling of various sports. PAC-10 men's basketball is usually on a Thursday/Saturday rotation with some exceptions.
Mondays - ACC women's sports
Tuesdays - ACC men's basketball
Wednesday - ACC/PAC-10 men's sports
Thursdays - PAC-10 men's baskeball
Fridays - ACC women's sports
Saturday - during football: 12pm ACC, 3:30pm ACC or PAC-10, 7pm ACC or PAC-10, 10:15pm PAC-10), during basketball a mix of ACC and PAC-10 men's and women's action
Sunday - mix of ACC and PAC-10 men's and women's action
Also, the ACC contracts expire after 2010-11, the PAC-10 expires one year later. Depending on the part that is picked, a joint venture might require a one year extension of the ACC's deal or some other awkward arrangement for a year.