A friend pointed me to news that Magento, a leading open-source commerce platform, has cracked 500,000 downloads, not to mention its 44,000 community members that have translated the project into over 60 languages. That is progress that money can't buy, or at least not cheaply.
But that's only half the story. It has been said that "imitation is the sincerest form of flattery," and the real story behind Magento's success is that it's breeding copycats. Several proprietary competitors, like Oxid eShop, are throwing in the towel and open sourcing their code, too.
Earlier this year I talked up Varien/Magento as a company and project to watch. I was speculating at that time, but today its success seems relatively sure. It's now a question of "how big?" for Magento, not "will it take off?"