It was funny I was at the UK Hadoop User Group a couple of days before this feature was announced. As Tom says in the article this was a feature that people wanted for Hadoop and then as if by magic it appears.
i wouldnt use hdfs just for added reliability, you could soft raid for that. but if you are working on any map/reduce type problems hadoop is a great way to go.
ive been saying it for a long time now, but damn... it's such a great time to be a developer.
Tom has done a really great breakdown of why it's useful. I would also really recommend watching his talk from the usergroup http://skillsmatter.com/podcast/cloud-grid/hadoop-on-amazon-... .
I also did a blog post for YDN which has a video with some more thoughts from Tom and other people http://developer.yahoo.net/blog/archives/2008/08/uk_hadoop_u... .