At HubSpot, we use MySQL a lot (and more every day), and most of our MySQL servers live on Amazon's Elastic Cloud. We use Amazon's Elastic Block Storage (EBS) storage service to store the database files and data.
I wanted to point out a very useful set of scripts, from Eric Hammond and Assaf Arkin (my fellow Apache committer). These scripts, one in Perl and one in Ruby, will take care of creating snapshots of MySQL EBS volumes for you, post the snapshots to Amazon S3 if you want, and discard old snapshots if you'd like.
Eric's Creating Consistent EBS Snapshots with MySQL and XFS on EC2, and Assaf's MySQL backups with EBS snapshots.
I hope you find these as useful as we have. Thanks, Assaf and Eric!