Sam,
Hadoop does appear to be the leading the charge for the standard for cloud storage using HDFS. There are a number of interesting extensions to it, including Hive, Pig, HBase, as well as MapReduce. It's support by Yahoo is important.
While Hadoop is an open source Apache project, Cloudera is adopting the now time-honored position of providing fee-based support and training.
I don't know for a fact if the AWS MapReduce service is based on Hadoop, but that would be my presumption.
Most position descriptions for cloud development engineers and architects (public, private or hybrid) now expect working experience with Hadoop and MapReduce.
Regards,
Fred.
PS: In terms of cloud storage interoperability, stay tuned for
JClouds