Join the crowd...I'm beginning to feel like I live there! Let's see...Stockholm, Copenhagen, Oslo, Paris, Brussels, Venice, Bologna, Verona and coming up soon (reserved already) for Lisbon, Porto and Barcelona.
The sum of my experiences so far is that a) it works, and very well, b) prices are generally better than traditional agencies, c) there are more opportunities for real connections with hosts, and d) IKEA has sold an awful lot of furniture all over Europe!
Seriously, AirBnB takes a lot of the hassle out of apartment rental. You reserve on their website; if the host agrees, you get a confirmation and AirBnB charges your credit card of PayPal. The host gets paid AFTER you have checked in, so if things are badly wrong you call AirBnB's 24-hour number and they find a resolution.
A lot different from the days of sending wire transfers and leases and insurance contracts back-and-forth. The website is well-organized, with pictures, amenities, maps and all the rest; more and more of the pictures carry a "Verified" mark that indicates they were taken by photographers hired by AirBnB (although I never had a false picture on ones that weren't).
Once you have the reservation--and not before--you and the host have each other's e-mail and phones, and can arrange keys, get information, ask questions and more. I've usually found that a real e-mail relationship develops, and when the host is nearby (happens often) the richness of information exceeds any guidebook.
Each apartment listing has a page for any additional notes from the host, but it's important to look carefully at the cancellation conditions...there are three different versions. One is very loose; you can cancel quite late without penalty. Another allows cancellation up to a certain number of days before, and the "strict" policy pretty much holds you once committed. The first two are the most common, but be sure to check which one you are signing up for.
When you sign up, there's a verification process...including checking you against credit cards, social networks and more. After you've stayed, you're asked to review your experience three ways: one for public, one for any private comments to the host, and one for anything you want to tell AirBnB but not share with host or public.
It's not just apartments, by the way...all kinds of spots, from a couch to a room to a house or houseboat and even a few trailers!