WordPress founder Matt Mullenweg has given his 2011 State of the Word address, and the state of the word is strong. Nearly 15% of the world’s websites are powered by WordPress, up from 8.5% last year. For every 100 new active domains in the U.S., 22 of them run the popular open-source blogging software.

Mullenweg’s address at the WordCamp conference in San Francisco this week goes through the history of the WordPress user interface, showing how its features developed over time and were then pared down to today’s minimal, efficient design. With its frequent adjustments to UI and its healthy market for ready-made and custom themes and plug-ins, WordPress’ user friendliness is key to its broad and rapid adoption by content creators. But this year, WordPress conducted its first user and developer survey, receiving over 18,000 responses, and it found a thriving economy for developers and site administrators as well.

6,800 self-employed developers who responded have built 170,000 sites between them, and their median hourly rate is $50. That’s good work, and if you can learn it, you can get it. The open-source content management system is driven by its independent developers, and it looks like there’s more work for them all the time.

In keeping with its open-source mentality, WordPress has made the survey data available here for anyone to root through. Mullenweg shares more about current and future developments at WordPress in the full 30-minute address, which you can watch here:

Have you used WordPress? Are you a WordPress developer? Tell us about it in the comments.