What's the Missing Authentication for S3 to Google Storage using gsutil?

There are lots of posting about copying over from S3 to GS, but I'm stumped on this one - all the authentication seems to be correct, what am I missing?

$ gsutil -m cp -r s3://ws-logs gs://ws-logs
AccessDeniedException: 403 AccessDenied
<?xml version="1.0" encoding="UTF-8"?>
<Error><Code>AccessDenied</Code><Message>Access Denied</Message><RequestId>659EC2ADB59407E2</RequestId><HostId>mTnCaiVt0elcnN7eljLvmiwqPwQui6Hr/VPSrR3pKT1TpjQaqRo3ZKeNloa9QU9DjzTcQE+Fc1g=</HostId></Error>
CommandException: 1 file/object could not be transferred.

$ gsutil -m cp -r test.txt gs://ws-logs
Copying file://test.txt [Content-Type=text/plain]...

$ aws s3 ls ws-logs
                           PRE dt=2012-12-01/

                           [ lots more entries ]

So, as you can see, I can create an entry in my gs bucket, and I can list my S3 directories. Is there something else I'm missing?