I would like to offer a contrarian view. Gittip is a nice initiative, in the "thank you for developing this project" kind of way - but I doubt anyone believes they can (or will be able to) pay the rent with donations paid through it. I wrote a post on this subject a couple of months ago, title "Open-source can't live on donations alone" [1].
I also don't subscribe to the notion that open-source should only be about the love - if companies like MySQL and Red Hat can make it into a huge business, and with the immense value open-source provides to the software industry, open-source developers should be treated as first-class citizens, not relegated to volunteer work late at nights, while doing their real job during the day.
Of course I'm biased, since I'm the founder of a company who's making that change happen. We started Binpress [2] to help developers build profitable businesses like MySQL and Red Hat around their open-source code. We do it by providing them with a platform for adding a commercial layer over their open-source code (whether it's self hosted or on GitHub, etc.), through commercial licensing and by providing customization, integration and support services.
We are a distribution marketplace, similar to the appstore or Steam but for open-source code products. We already have many developers making silicon-valley salaries working exclusively on their open-source projects - and we're just getting started. We've been bootstrapped (and profitable) for 2 years but are now closing our seed (after going through the 500startup program).
If any of this makes sense to you, you are welcome to reach out to me at eran@binpress.com (I'm Eran, the CTO and co-founder).
[1] http://www.binpress.com/blog/2013/04/14/open-source-cannot-l...
[2] http://www.binpress.com