Anyone have any experience running MGOS from an EC2 instance? I'm
mainly looking for some rough idea on the cost...though I'd also be
interested in knowing if there's a way to store and access MGOS data
from S3 via EC2.
As for storing your data in S3, I think you would have to figure out how to configure your Unmanaged Data Mappings (and/or if using tiles, your tilecache path)on the MapGuide server to access your S3 bucket . Speaking from experience, I know that you can include UNC or drive paths in your serverconfig.ini configuration (on a Windows machine), but what about the S3 bucket? Remember, MapGuide is consuming whatever the server has access to. However, I don't think you can access S3 buckets as a networked drive without a 3rd party application. I'd be curious what others have found.
Also, see first link above for alternatives to amazon.