The best open-source projects have little problem with adoption. Their problem, increasingly, centers on monetization of their popularity. From Drupal to MySQL to Audacity, sometimes the best things in life truly are free...which can be a problem. The solution, however, may be cloud computing.
I've articulated this before, but theory met reality this past week with announcements from DimDim, an open-source Web conferencing provider, and Acquia, the focal point for Drupal support and value-adding services. Both have interesting new cloud strategies that promise to deliver customer value while funding the vendors' payroll.