If you're wondering what's up with Ruby-Amazon, it is actually based on Amazon Web Service's 3.1 version. I was playing with it earlier this week and realized there was a ton of missing data. So I've migrated some of my apps to Amazon-ECS as a result. I have to say I'm pretty impressed with the library as it allows you to flexibly integrate with new versions of Amazon's platform. There was some effort in integrating a different library but if you're familiar with Hpricot it should be a snap. I'm not sure why Herryanto built it with Hpricot, as I'm a REXML fan myself.
I totally dig Amazon's platform though. It really allows affiliates to add value to Amazon's site.