I can't see any advantage in using multiple keyspaces. It is highly unlikely that several applications would share the same Cassandra cluster in any nontrivial deployment.
Things more important than replication-factor, such as partitioner and ring token distribution would be compromised by several apps sharing the same cluster. Moreover, an application which was using Cassandra is likely to have so much data to store that it can usefully benefit from many dedicated nodes. If you did decide that multiple keyspaces was the right thing to do, your client tasks can simply maintain several connections to them (if they individually need >1); this should not be a problem. Mark
