I recently came across an article referenced in sqlservercentral.com which talks about Hadoop and ETL. The article focuses on some of the misconceptions surrounding how Hadoop might replace ETL. Hadoop and ETL are complimentary to each other since each have their own space. Please refer to the article here:
http://blogs.computerworlduk.com/idc-insight/2012/01/the-rise-of-hadoop-is-etl-dead/index.htm. The article very nicely lists the pros and cons of hadoop at a high level, also how ETL is here to enable datawarehouses which handle structured data.