Enterprise Java was becoming mainstream, but the open-source community saw that it had much more potential than the tools provided by Sun.
Codehaus provides project hosting (source control, issue tracking, websites, continuous builds, downloads, mailing lists, IRC, etc). This was back before GitHub existed and the only other option was SourceForge (which was terrible).
But above all, Codehaus provided community. The developers across projects all hung out together, on mailing lists, IRC and the occasional global meetup. Respect and friendship. It was there that many gripes and problems were discussed and new projects were born.
If you've ever benefitted from Groovy, Jetty, Grails, Gradle, XDoclet, XStream, jMock, EasyMock, QDox, Drools, Esper, Mule, PicoContainer, Jackson, Janino, JBehave, Stomp (and hundreds others), this was thanks to the Codehaus community.
Many of the projects and people have gone on to do great things. Companies have been formed. New communities created. Many projects died, some thrived. Codehaus is no longer the hotness it once was, but it provided the foundation that many of us have benefitted greatly form, and it's no doubt one of the giants that the Java open-source community is standing on the shoulders of.
Codehaus is now shutting down: http://codehaus.org Please join me in raising your glasses to the people and projects. Codehaus, we salute you. So long, and thanks for all the fish.