Some one posted a presentation[1] by Jonathan Ellis from the August user group in Austin, TX. For those unfamiliar with him, Jonathan Ellis is the Cassandra project lead and CTO of DataStax. It runs for about 1.5 hours but is really informative. He covers things introduced in 1.2.x as well as new features in 2.0 like triggers and light weight transactions.

[1] http://youtu.be/sJJzDB9RhzA