Novels written by groups are generally unreadable. This is because they have no focus, and because the immediate cheap laugh always wins. It's a shame, because with a little more forethought, such shortcomings could be fixed. Ie: start by communally developing an outline, main characters, etc. It would also be interesting to use Mechanical Turk in a systemic way to have "the crowd" determine which of several proposed plot-points is most consistent with the whole, etc.