I know a number of people that essentially swear by it, but my personal experience has been less than stellar. I spent two weeks travelling Europe this past spring and wanted to couchsurf the whole way. Unfortunately, I was only every able to find an opening for the two nights i was spending in Dublin at the end of my trip. I was flying through Dublin at the beginning as well with a 9 hour layover so I went into the city and met up with the guy I was going to be staying with. He seemed like a nice enough guy, but when I got back to Dublin two weeks later I was unable to get a hold of him. His phone went to voicemail, he didn't respond to emails, and his couchsurfing.com account had been deleted! I ended up staying at a hostel, which was fine but annoying since it was a last minute change and I couldn't even get the same bed for both nights.
I'd say it's worth a shot, but be prepared to be flexible and scout out local hostels as backup (if you're going to be in Vienna and/or Munich I highly recomment the Wombat's hostels; also if you're going to be in Munich you should take the free walking tour from the Munich Wombat's lobby (you don't need to be a guest), if it works with your schedule try and take the tour with Ozzy, I think his tour is the Friday one, but just ask at the front desk).