We recently did a performance evaluation comparing Hypertable with HBase.  I thought users of this list might find the results interesting.  The test report can be found through the following link:

http://www.hypertable.com/pub/perfeval/test1/

Hypertable runs well on top of KFS and the latest binary packages include a KFS 0.5 broker.  The Hypertable Manual describes how to install and setup Hypertable and Up and Running with KFS has more information about running Hypertable on top of KFS.

- Doug