I don't know if this is the right way to go about it, but I thought I'd do a pull request.
I fixed so that the RackspaceServerList class correctly parses the server info.
Fixed Chef::Knife::RackspaceServerList to handle the v2 responses.
Thanks for the pull request, I'm actually coding on this right now and have already fixed that part. If you're in IRC or have some other IM protocol available I'd be happy to collaborate on what I'm doing right now.
Name your Freenode channel of choice :p
I should be easy to find. #ruby-fog, #csbeta, #chef, #chef-hacking and 10 others as 'mattray'