Hiya,
I've signed up for the UK version of Rackspace Cloud Files, which is exactly the same from a frontend perspective but must be doing something slightly different under the hood because this plugin completely fails to recognise the API key and username.
AFAIK Rackspace use exactly the same system, but the central server for those who create UK accounts is in London rather than the US. They also have a full UK-based support team, etc. I asked and there's no way to transition a US account to the UK system at this time or vice-versa.
Also of note is that the UK version uses the following URL format:
