Orion Henry at Heroku wrote about this and described different software RAID configurations and the performance characteristics of each a while back:
http://orion.heroku.com/past/2009/7/29/io_performance_on_ebs...
http://orion.heroku.com/past/2009/7/29/io_performance_on_ebs...
Plus, that's a year old, would love to see some updated advice. You'd think Amazon would write more guides like this.
Despite being relatively old, I think the advice and approach still holds. Clearly, EBS hasn't improved since then and the need to do this kind of striping over EBS volumes hasn't been obviated yet.