[shykes]

One word of caution: sometimes when an instance becomes unavailable (think network partitioning), all its EBS volumes will become unavailable as well. You can't snapshot, you can't detach. My most frustrating experience on EC2 yet.

[JeffJenkins]

You can force detach using the console tools. I had this problem too

[shykes]

I can remember at least one case where force-detach didn't work either. In that case there is absolutely nothing you can do to access your data.