I just installed and am working with Alfresco (alfresco-tomcat-1.0.0rc1b), on my RedHat Linux system - looks to be a very nice CMS - I've worked extensively with Documentum and so far I think this is laid out as a much nicer, easier-to understand Enterprise CMS.
One comment (so far). One of the first things that appear after logging in is an "Alfresco Tutorial", presented as a PDF file - clicking on the link returns "The node's content is missing … Please contact your system administrator". I searched through the Alfresco download and there is no PDF by that name - as first appearances can be critical, I suggest it would be a good idea to fix this (I understand it's very early in the beta-release process - just an observation).
-Mick