I use libcloud extensively for public and private EC2 clouds, as well as Rackspace. However, I have had no success whatsoever in using libcloud to access either Terremark or Virtacore.
My only requirement is that I can log in and list instances that are running (vApps in vCloud lingo). With Terremark, after the initial login, I get a 401 error. I believe that this error is not a session cookie issue, but is more in line with the code logic going through vCloud object layers in an attempt to list nodes.
With Virtacore, I cannot even log in.
It is possible that both vendors have deviated from the vCloud Express API. However, I have Googled everything I can think of and I cannot find a single code example that uses libcloud to access either vendor. A simple example that shows how to list nodes on Terremark would suffice.