If you have read my comments on Alfresco, you probably noticed me mention that Alfresco is not all open source. In fact, I have said the "E" of their ECM was closed source because the features that an enterprise would need (LDAP integration, group based permissioning, etc.) were only available in the for-pay version.
Alfresco's recent announcement shows a change in their licensing model which makes the entire code base open source (licensed under the MPL). The Enterprise and Community versions will have the same functionality but only the Enterprise version will be certified. The Community version will be more oriented toward research and development and undergo less QA. This is similar to the relationship between Fedora and Red Hat Linux Enterprise Linux.
It is unclear what the difference in quality and reliability between these two versions will be. Alfresco strongly urges anyone using the software for non-experimental purposes to use the Enterprise version but says the Community version is a great low risk way to try the software and see if it works within your enterprise. This sounds a little like the ShareWare model but it does give companies the choice to release themselves from paying the Enterprise subscription if they feel like they are not getting the value out of it. The absence of lock-in is certainly a big benefit. Who knows, maybe some other company will step up and specialize in supporting the Community version. Open source is all about choices.
Another potential benefit of this move is that it may give a developer community a chance to grow around Alfresco. Before the licensing change, there was little incentive for an independent developer to contribute code if it could wind up in the for pay version. If a developer community does take root, the community version could become a viable option for enterprises in much the same way that there are many production servers running Fedora and openSUSE.
I think that this was a necessary step for Alfresco and I am glad that they did it. The only challenge is how their marketing department will create messaging around the difference. How will they encourage people to buy the Enterprise version without derogating the Community version?