Janus, while you are certainly correct that looking at revenues gives a different picture than looking at adoption, I still believe that revenues are the most important metric. Why? One reason is that the time-tested competitive strategy of undercutting a market leader with discounted or free alternatives is ultimately a sales strategy. The hope of course is that the money left on the table in the short term will be made up in the long term via market share gains. The revenue numbers, however imprecise, are still the best indicator of when or if that strategy will pay off. I believe this is true for for-profit open source companies as well; altruistic motivations aside, they are still in business to make money. Support and maintenance revenue is included in Gartner’s market sizing. When an open source company chooses to charge only for support and maintenance and not for licenses, that too is a sales strategy whose success or failure will ultimately be reflected in the revenue numbers.

Certainly adoption is also a very important metric. But for my “money” the value the market places on these products provides the clearest picture of what’s currently happening. The adoption trends you describe are likely predictive of future changes to the revenue picture.