Matt Asay blogged about recent research suggesting that much of the core development work on open-source projects is done by paid developers.
It's interesting to consider this in the light of Drupal. Drupal has lots of contributors who are totally volunteer - and they've been contributing to Drupal for a long time. Yet, there are Drupal developers who work for places that pay them to develop sites and functionality on Drupal - even though those companies aren't the one who offer Drupal in some commercial way (the way Alfresco does for Alfresco).
I don't know whether this will change for