That may or may not be true - they have open-sourced several large projects. Flex (http://www.adobe.com/products/flex.html), for example is a big software product that Adobe switched to open source in 2007.
From an article back then:
"Ward outlined the transition as having the following steps:
Today - Creation of Mailing List for Discussion
Summer 2007 - Public Bug Database and Daily Builds
Second Half 2007 - Flex 3 Released
December 2007 - Read Only SVN Access, Patches Welcome
2008 - Committers with Write Access, Creation of Possible Subprojects "