I don't go as far as strcitly using open source, but I've managed to improve my productivity with a lot of open source software. To me, the software I use is just well designed, quick, and hackable. The only non-open source software I still use is the one included with Ubuntu, the one in my cell phone (non-smartphone (runs java)), my appliances (Linux probably, not no source), and the code that runs in my cars computer. Could I survive without closed software? Not yet. Though I keep looking for ways to replace closed systems with open ones.