My gripe with Airbnb is the option for a basically no penalty cancellation by a host. Sure, they give you a little extra to cover the cost of finding another one, but the hassles made me seriously annoyed. I had two hosts cancel a reservation recently. The second host was actually a replacement for the first host who cancelled. And I'm a guest that has good reviews... wish they held their hosts to a higher standard when it came to cancellations (e.g., blocked for x months if hosts cancel y times within a z month period).
I have used Airbnb five trips so far, and had three cancellations by hosts that had to be rebooked. So far not over the top enthusiastic. The only reason I keep going back is to find places that have kitchen to cut down on eating out costs while traveling (plus, healthier food).