re: HBase: Hadoop's Next Big Data Chapter
It's true that HBase provides ACID guarantees. However, atomicity is limited to changes in a single row. Updates that touch multiple rows are not guaranteed to happen atomically. Given the flexible data model you get from column families, this might be OK for many applications where scale and write speed are more important than multi-row transactions. However, this is nothing like the atomicity you get from a more mature transactional system.