Who Runs What Hypervisor?

Have you taken any time to so who run what hypervisor? Is it just me or does there seem to be a lot of articles and post about Open Stack recently that it would almost seem like everything is running on Open Stack? Seems to be that there seems to be a push to help keep Open Stack on the path to becoming more mainstream and the new partnership with Red Hat building might be just the ticket. For now, Open Stack is still going through its adolescence but has great potential to go out and really make a difference in this world. Until then, have you ever stopped to consider and look at what underlying hypervisor is supporting the clouds we all know and love?