After a few weeks with a "Beta has expired" message, and no new beta to download, looks like MS has gotten their act together and released Beta 3 of the RDP Mac Client.
Now the question is, is this a new beta with actual changes, or just the same software with the expiry date removed? Being that the only information about the beta is here there's no actual information about any changes. Oh, and the 'feedback' link to read the forums about it doesn't work. *sigh*
If you're looking for an alternative (if you hadn't found one already), the de-facto seems to be CoRD, which I've played with a bit.