We moved our development and production systems to AWS in 2008 and have been quite happy. It has allowed us to grow and scale with load on production and quickly test things in development. There a few things to keep in-mind. First, if you know your usage pattern and can drop some money upfront then utilize the reserved instances to save some money. Second, you will need a script management system of some kind to run on the virtual servers at boot/shutdown, I recommend using something like Rightscale or Scalr. Most importantly, don't do it without some experienced help for the setup, a day of a consultant's or system admin's time to walk through your migration plan with you will save you a lot of help down the road. Lastly, aws has a cost estimator that is quite helpful.