I've used AirBnB Numerous times since their inception across multiple countries.
As a solo Traveler: Super Cheap but small bedroom in a small apartment in London Proper. close to everything, $50 ish US a night. Got a beer with the Host, good 1st experience.
Liverpool: Very nice private room and i think private shower, with toiletries and tea/coffee and snacks with bottled water included. $49 for the one night, but there was a full day of cool stuff to see/do in Liverpool, and I needed it for a connecting flight to Dublin for $25.
Dublin: Very average to 'could use some decor tips' bedroom in a house with 3 other dudes. Same price, but it was in the heart of Dublin.
- Bonus - Going out with a local and his friends (owner /roommates, 2 of non-Irish decent) was MUCH More fun than going to a bar solo. Maybe I'm not the best Solo-Bar-hopper but this experience made up for the lackluster bedroom... which was only used for sleeping anyways.
- - -
With the Wife in Japan:
Tokyo - Best Trip Ever. The hosts were just like us, hard working 'regular' folk, who lived in Shinju-ku (Tokyo) - which itself was a cool part of Tokyo. The SUPER Value came from A) being near the Trains B) Getting a Free/included Portable WiFi which was incredible C) getting Free dinner and or breakfast EVERY Day - in a place where dining out is kind of expensive and D) Advice... Just like having an in house concierge. They joined us out a couple of times, told us what we were getting into when we asked about lines / costs / crowds of ANY given thing, anywhere. They were AirBnB Super Hosts tho ($99 a night, during Cherry Blossom Season)
* - We lost some luggage presumably at their place... they couldnt find it, and when we got home, they had already sent us a box of stuff we said we lost (magnets, shot glass and snacks from different cities).
Osaka - Had a small apartment with a nice bathroom and kitchen. We used the kitchen to make an AMAZING $30 Kobe Beef steak dinner... twice. It was incredible.
California Coast - Great options for doing the 'Redwoods Hikes' or 'Trip down the Coastal highway. Did one in Oregon that was $99, but that one included a bottle of wine, a master bed with an attached outdoor jacuzzi and a view of the Damn ocean. The CA ones were just regular houses for $39 short notice.
I have yet to have a bad experience. All you have to do is 'read' into the personality of your host and their reviews.
TL
R - AirBnB is great.