I've been a host now for about 9 months. We have had almost all positive experiences (except for the one lady who begged to bring her "well behaved" dogs... but I digress). I am fine with the way the reviews are set up, I think it keeps people honest. A couple of suggestions for folks using Airbnb: (1) don't wait until the night before your visit to try to book a room. Even a usually conscientious host can forget to check their email. (2) ask questions before you book. (3) book a place where the pics were taken BY Airbnb, that helps reduce the chance of scamming (and if you're a host, at least last year it was free).
My only real complaint is their claim that they "can't" transfer the money to you over the weekend; so if you have someone at your place Friday - Monday, you probably won't see the $ in your acct until Tuesday. We are in a 24-7 financial market, I'm sure they could fix that if they wanted to.
I for one hope that (a) the # of negatives reflects the fact that people are more likely to share those than take the time to share positives; and (b) airbnb does address what seem to be some fixable situations so that I as a host can continue to meet and host folks from all around the world.