It is far more complex to measure outcomes as a result of insights generated from the community.
A community can provide an early warning system to products, generate valuable feedback, suggest new features, show trending topics, yield valuable qualitative and quantitative data. This can reduce time to market, validate ideas, shorten feedback loops, etc. Better yet, if the community generates a killer idea, the value of this is hard to quantify.
Another example comes from television show producers who use the number of pirate shows by online communities (often their community) to estimate popularity and make informed decisions about licensing deals. This is hard to equate to any other metric.
We have determined some of these categories, such as early warning of possible problems, while identifying and fixing bugs are already factored into customer satisfaction and retention.