As I mentioned a few times recently, last week I gave a presentation in the open source track for Oracle OpenWorld 2006. The topic was using open source in the enterprise, tracking guidelines an advice for enterprises getting more and more involved in open source. It goes from using open source to a company either starting their own open source project or getting heavily involved in one.
In my mind, enterprises are the ones who benefit most from open source, but my sense is that there isn't enough evangelizing of using open source to enterprises. There are very vocal evangelists, but not enough. Most of the effort to date has been spent on vendors, which is great. As RedMonk has found and helped people find, vendors certainly can benefit enormously if they figure out either "blending" open and closed source or making the jump to "pure" open source.