Ideally centralizing payment and identity verification to a 3rd party is a step up from Craigslist where you have to do it all yourself. EJ stated that AirBNB does not give out contact information until after someone's rented the place, preventing screening applicants.
However from the terms (keep in mind they may have changed it since EJ's case):
"1.2 Identity Verification. We make no attempt to confirm, and do not confirm, any user's purported identity. You are responsible for determining the identity and suitability of others who you may contact by means of this Site. We do not endorse any persons who use or register for our Services, whether as guests or hosts. We do not investigate any user's reputation, conduct, morality, criminal background, or verify the information that any user submits to the Site. We encourage you to communicate directly with potential hosts and guests through the tools available on the Site and to review your hosts’ and guests’ profile pages for feedback from other users.
13.1 IF YOU USE OUR SERVICES, YOU DO SO AT YOUR SOLE RISK. YOU ACKNOWLEDGE AND AGREE THAT Airbnb DOES NOT CHECK ANY GUEST, HOST, OR OTHER USER’S BACKGROUND OR RECORD. Airbnb IS A REPUTATION-BASED SYSTEM. TAKE ADVANTAGE OF OTHER USER’S COMMENTS AND THIRD-PARTY REFERRALS ON HOSTS AND GUESTS. USE COMMON SENSE. BE AWARE AND BE SAFE. OUR SERVICES ARE PROVIDED ON AN "AS IS" AND "AS AVAILABLE" BASIS. WE EXPRESSLY DISCLAIM, AND YOU WAIVE, ALL WARRANTIES OF ANY KIND, WHETHER EXPRESS OR IMPLIED, INCLUDING, WITHOUT LIMITATION, IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
14.1 WE SHALL NOT BE LIABLE FOR DAMAGES OF ANY KIND (INCLUDING, BUT NOT LIMITED TO, ANY DIRECT, INCIDENTAL, GENERAL, SPECIAL, CONSEQUENTIAL, EXEMPLARY OR PUNITIVE DAMAGES) EVEN IF WE HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES, ARISING FROM OR RELATING TO: (A) THE USE OR INABILITY TO USE OUR SERVICES; (B) HARM OR DAMAGE TO YOUR PROPERTY AS A RESULT OF USING OUR SERVICES; (C) DISCLOSURE OF, UNAUTHORIZED ACCESS TO OR ALTERATION OF YOUR CONTENT; (D) ANY HARM TO YOU CAUSED IN WHOLE OR PART BY A THIRD PARTY, INCLUDING BUT NOT LIMITED TO ANOTHER USER OF THE SERVICES; (E) STATEMENTS, CONDUCT OR OMISSIONS OF ANY GUEST, HOST, OR OTHER THIRD PARTIES ON OUR SERVICES; OR (F) YOUR OR ANYONE ELSE'S CONDUCT OR ACTS IN CONNECTION WITH THE USE OF THE SERVICES, INCLUDING WITHOUT LIMITATION FROM INTERACTIONS WITH OTHER USERS OF OUR SERVICES OR PERSONS INTRODUCED TO YOU BY OUR SERVICES, WHETHER ON-LINE OR OFF-LINE."
In essence, I find it hard to understand what added value AirBNB provides over either Craigslist (pay) or Couch Surfing (free, reputation-based).