I can't help but be a little surprised that Heroku's entire build system is disabled by an S3 failure in one region. Now I'm unable to add a notice about the issues to my site's HTML...
Since S3 is the defacto artifact delivery system for most people that run on AWS, it's not much of a surprise. For the most part, very isolated incidents aside, S3 is rock solid. Even EC2 relies on S3 for launching non-EBS instances.