Amazon SimpleDB

I'm a big fan of Amazon EC2 and S3. To be able to use the amount of computing power you need and the amount of storage you need and only pay for what you use is a good way of computing in my view. However, EC2 wasn't built to run clustered databases like MySQL on, and I've had problems finding any service that will let me pay for the capacity I need (cpu time and disk space) and give me a guaranteed query time. Amazon's SimpleDB seems to be a good step in that direction, and I'm really looking forward to toying with it and hopefully use it for many interesting projects.