My girlfriend has the brown one, I have the black.
I actually like the brown one quite a bit - it's a lighter reddish brown in person. I probably would have bought it if my girlfriend hadn't bought hers first (silly issue - just wanted a way to easily tell which was which). The contrast stitching of the black looks silly and I quickly dyed it with shoe polish.
Generally with tech stuff in the business world people tend to prefer black. Full disclosure - I'm a denizen of StyleForum where black is anathema for fine leather goods... bags, shoes, belts, coats, etc, (connotation - black is too conservative/boring/no imagination) so given the choice I tend to pick brown. I now rock a Vaja Agenda 2 in dark brown.