Wanted to let everyone know that if you go to the Cassandra website (cassandra.apache.org), you'll notice that there has been some change. Outside of a face lift, the main change is a much improved documentation section (http://cassandra.apache.org/doc/). As indicated, that documentation is a work-in-progress and still has a few missing section. That documentation is maintained in-tree and contributions (through JIRA as any other contribution) is more than welcome.
Best, On behalf of the Apache Cassandra developers.