I would do it and just be selective. The idea was originally that travellers open up their homes to other travellers to make it more affordable - with the idea that you treat their home as if you were a guest (and not like a hotel). Lately, it's become a boutique guesthouse sort of thing but you can still find basic listings. You can even get AirBnB to hire a professional photographer for free. They took amazing pictures of my place.
I convinced my friend in Stockholm to do it. She'd pay off her monthly rent by putting it up for 3-4 days and crashing with a friend. I don't know what you're paying for rent/mortgage, but chances are that you'd be able to pay it off for the month & then some if you're putting it up for 3 weeks. I'm sure YMMV and all of that...but I'm also pretty sure there's some sort of insurance. You can charge a cleaning fee if you want and just pay someone to clean everything when you get back. It can actually be quite lucrative in big cities if you don't mind cleaning up after people. Responding to retarded questions throughout the day gets tiring if you have a 9-5, though.
And for the other guy that made the other thread, absolutely use it. If you'd pay 170 for a hotel room, you could rent an entire flat/house/etc. to yourself for that much a night.