I'm not defending a post-scarcity future (I think it's highly unlikely), however, people are not necessarily motivated purely by monetary incentives. Check out this video on the topic:

http://www.youtube.com/watch?v=u6XAPnuFjJc

There's a Sci-Fi book called Accelerando, by Charles Stross; he released it under the Creative Commons license, so it's available to freely download as an ebook. It's a pretty interesting futurist perspective, and the first couple chapters deal almost exclusively with a new global economy in a post-scarcity world.

Post-scarcity is more than just 'welfare on a larger scale'. It's an upending of "Supply and Demand". Money works because of supply and demand; post-scarcity imagines a future with sufficiently efficient automation, resources and energy supplies to make money irrelevant.

For now, though, this idea is relegated to Sci-Fi books. I don't foresee it becoming a reality anytime soon.