Wow, I love the simplicity that ZooKeeper brings to a really hard set of distributed problems. Check out this Introductory Video that explains it more in depth. Basically group leadership/coordination and cluster wide configuration issues are taken care of if you Use ZooKeeper.

The Apache Geronimo project has recently changed it’s commit policy to a Review then Commit (RTC) policy. Which means no one can commit to the Geronimo project unless you submit a patch and then get 3 other Geronimo committers to review, apply, test, and then give you 3 +1s.