What Does Open Source Need for Mainstream Desktop?

HesAnIndieRocker asks: "So what will it take to make open source technology a mainstream alternative on the PC desktop? It feels like we've been on the cusp for many years now and the applications available for most common tasks are certainly competitive, but we still hover around a 5% market share by most accounts. I've recently written an article in my weblog about some possibilities, but I'd love to hear what others think."