Last week, .Mac users were having trouble using Microsoft's Windows Live Messenger service (why they don't connect to MSN Messenger with Adium is unclear, but, whatever...). Specifically, attempts to connect with an "@mac.com" email address produced an error, prompting the the user to change their address.
Microsoft has since fixed the problem, which they attributed to "...internal error during routine testing." In other words, you're now good to go, .Mac users. All is well that ends well.