From this list and the NYC* conference it seems that the consensus configuration of C* on EC2 is to put the data on an ephemeral drive and then periodically back it the drive to S3...relying on C*'s inherent fault tolerance to deal with any data loss.

Fine, and we're doing this...but we find that transfer rates from S3 back to a rebooted server instance are very 15 MB/second or roughly a minute per gigabyte.  Calling EC2 support resulting in them saying "sorry, that's how it is".

I'm wondering if anyone a) has found a faster way to transfer to S3, or b) do people skip backups altogether except for huge outages and just let rebooted server instances come up empty to repopulate via C*?

An alternative that we had explored for a while was to do a two stage backup:
1) copy a C* snapshot from the ephemeral drive to an EBS drive
2) do an EBS snapshot to S3.

The idea being that EBS is quite reliable, S3 is still the emergency backup and copying back from EBS to ephemeral is likely much faster than the 15 MB/sec we get from S3.