
Since I've been traveling full-time for a while now, I've had my fair share of ups and downs when it comes to furnished rentals. Usually, I'll do some research on various neighborhoods, sift through endless photos, and go with my gut on which apartment will serve us best.
One site that had proved itself vital this way of life is Airbnb. By providing a safety net in the peer-to-peer rental market, it gives me a certain piece of mind. However, Airbnb can't possibly fully vet all of the rentals before guests arrive, so here are my tips to ensure a fantastic stay before you pack your bags.
1. Have a back and forth exchange with your host before you book. Since you're staying in someone else's property, it's nice to get to know their personality before you make a commitment. Do they answer your questions in a timely fashion? Those that are slow to respond before you book may be reluctant to fix any issues you might have once you move in. Do they have specific and thorough responses to questions about wifi speed, public transportation and quality of neighborhood? If they don't, perhaps they have something to hide, or they're not investing in providing a stellar experience. Also, this process can weed out those who might seem a little shady, so trust your spidey sense! I've walked away from several transactions where the host wanted to take the payment process off of the Airbnb site.

2. Scour the photos and reviews with a keen eye. There are certain aspects of a property like noise level and smell that you can't decipher from a photo. Check for a general cleanliness, decent appliances and even neatness in the shots. If someone didn't bother to pick up their gym shoes before shooting photos, they might not give the bathroom a hearty scrubbing before you arrive. Look through reviews to see if others mentioned how well they slept, if the bed was comfortable or if they were kept awake from loud neighbors. Also, check out street view of the neighborhood and plug the location into Walk Score to see what's nearby.

3. One reason I prefer Airbnb to some of its competitors is its customer service team. However, when contacting concierge or the help desk, keep in mind that you probably know the area where you are better than they do. Come to them with a specific solution to your problem and they'll be able to help you more quickly. Once, after a big storm in a rural area, I lost internet connectivity, and so did the entire region. I spoke with Airbnb and asked that they call a local hotel to see if I could work from their lobby. They made the call and worked out the details, but I had to have the solution at the ready.

Booking properties on Airbnb and other home stay sites is a bit more work than reserving a hotel or hostel, but the payoffs can be huge. For me, it's really worth it to have accommodations that feel a bit like home when traveling domestically or abroad.
(Images: Smith Schwartz, taken at Airbnb properties in Texas and Argentina)

Sprout Side Table
I actually used Airbnb while in Germany two weeks ago. I had no problem with the owners of the apartments. I was really impressed. Now there were two that I tried to contact and they never responded, but no big deal. It was a real money saver! Hotels in Germany are about 200+ a night and renting an apartment was 70.00 a night.
If you are travelling abroad, I would check out the site.
I've just listed my place on airbnb, and this is really helpful in helping me put my best foot forward! I do need to edit my photos on there, since I'm still in the process of prepping the room.
My husband, 3 year old and I LOVE airbnb. We are currently on a RTW trip, and have used the site to book our accommodations about 8 or 9 times now. True, it does take a little longer to book then a hotel room does (we usually do quite a bit of correspondence with a host since we are traveling with a small child), but we have had some amazing experiences we would have never had if we stayed in a hotel instead. Our past hosts invited us out for BBQs with their friends, threw our son a birthday party, even let us use another spare room in their home when I came down with a bad cold. Airbnb is probably the best option for anyone who really wants to blend in with the locals. PLUS my husband and I have really loved getting to "test drive" all sorts of home layouts, kitchen set ups etc.
If you would like to sneak a peak, you can find more about our trip here
http://absencealert.blogspot.com/
I've always used HomeAway, which does NOT help you in case of a crisis -- but they're upfront about it, and by using a variation of these tips, I've always gotten good apartments from reputable people. Best ever was in Vancouver; worst was in Woodstock, which was a cool place -- but the owner felt like she needed to show her decorator friend the place while I was in there, even though the apartment's booking schedule was free for the subsequent ten days. Hmmph. Going to try Airbnb next time!
My sister, cousin, & I used Airbnb when traveling to Washington, DC last year. It was cherry blossom season and we saved a TON in comparison to what the hotels in the area were charging. We were a little turned off at first by our host's communication before our arrival (not using complete sentences, used a lot of abbreviations, took multiple emails for her to address certain questions), but in the end we had zero problems with the property and she was very accommodating. I would not hesitate to use it again. You definitely get a better feel of being a local when you travel this way.
I have booked a number of places in Italy using airbnb for a trip that's coming up in a few weeks. I haven't used it before, but I'm confident about the bookings I've made - and excited about the trip.
We've been hosting and traveling on Airbnb for the past two years. In over 40+ guests, perhaps one or two were less than ideal, but mostly we've met very interesting people who take great care of the space and enjoy sitting down for a good chat. We keep our Airbnb rentals super clean and try to go out of our way to make people feel happy.
My travels with Airbnb have also been great, though I basically follow the process described above - spend some time on introductions to figure out if this is someone I might like to have a beer with and check to see if the place looks clean and homey. I think the introduction chit chat beforehand is especially important, particularly if you're staying in a room in someone's house.
Oh! And a bit of a sneaky tip: check to see who you're renting from/to by clicking on past reviews they got and looking up who posted them and what your potential guest/host wrote about them. It feels a little like internet stalking, or reading someone else's mail, but it's definitely helpful to know a little bit more about how they interact with others!
We've used AirBnB a few times in NYC with only good experiences. Next stop, AirBnB in Paris: http://richardtulloch.wordpress.com/2012/06/02/air-bnb-a-way-to-afford-paris/