16 prefixed reads get you all the logs for mydomain.com for that hour:

http://myserverlogs.s3.amazonaws.com?prefix=0/service_log.2012-02-27-23.com.mydomain

http://myserverlogs.s3.amazonaws.com?prefix=1/service_log.2012-02-27-23.com.mydomain

…

http://myserverlogs.s3.amazonaws.com?prefix=e/service_log.2012-02-27-23.com.mydomain

http://myserverlogs.s3.amazonaws.com?prefix=f/service_log.2012-02-27-23.com.mydomain