The cassandra issues were primarily ops failures, and secondarily an older version of Cassandra making it difficult to recover once it was overwhelmed. (Some of the resulting improvements in Cassandra are documented here: http://www.riptano.com/blog/whats-new-cassandra-065)

Cassandra looks to be working fine for reddit now: http://blog.reddit.com/2010/08/everything-went-better-than-e...