As you say, the real trouble with EBS is when serving application data. We run a lot of databases, and EBS was just not good enough for them even when there were no system-wide issues.
Our problem with EBS as a boot device was that occasional system logs, etc. would go it, and when EBS was down the inability to reach the disk (the block-store abstraction problem) would lock up the whole OS.
Our problem with EBS as a boot device was that occasional system logs, etc. would go it, and when EBS was down the inability to reach the disk (the block-store abstraction problem) would lock up the whole OS.