For all of us who have been mixing with a laptop or two laptops the answer to a true DVI a/b mixer has arrived.
I got to see this thing working in person while I was in Lisbon for a festival when Toby was on his way to Brazil to premier it with D-Fuse.
I you don't own a V4 and want to mix 2 laptop signals this is the one for you.
http://tobyz.net/tobyzstuff/projects/dvi-mixer