Six Apart will be releasing an open source version of their product Movable Type.  I think this is great.  Many in the blogosphere have said that Six Apart has been forced to move to open source because its largest competitor, WordPress, is open source.  (Both WordPress and Movable Type are blogging platforms.)  Maybe.  Maybe customers had gotten used to WordPress' modularity and wanted the same from Movable Type.  On the Movable Type website they say that their customers wanted an open source version:

our customers and our community have asked for an open source version of Movable Type.  Many customers and developers in the Movable Type community were looking for a version of Movable Type that they were free to modify for their own needs.  Additionally, there are community members who are looking to bundle an open source distribution of Movable Type with other open source products.

It's hard for an existing product to release as open source - what are people supposed to work on, fixing bugs?  But in the case of Movable Type, I think they will benefit from the WordPress model.  People know what blog plug-ins should look like.  They know what they can add to the Movable Type platform.

I think I'm a case in point that Six Apart will keep and make new customers by being open source.  I've been debating moving my personal blog from the Six Apart platform to WordPress because I love all the plug-ins that exist for WordPress.  But I love the Six Apart support service - I regularly dig myself into big trouble trying out new things and they always help me set things straight again.  Six Apart has been adding plug-ins and new features to their platform and hopefully now that they are open source the number of new plug-ins will grow even faster!

P.S.  This blog uses WordPress.