I know we're currently seeing folks having a problem logging into the site by means of Windows Live accounts. Unfortunately, the problem is on Microsoft's end - we've submitted a ticket.
In the meantime, I want to point out a neat feature that can help: You can log in using a different social account, and if it or you provides the same e-mail address that you use with your Live account, our site will link the two. From then on you can log into the same profile on our site using either social account. Makes a nice backup.
For this linking to work, you (a) need to know the e-mail address that you use to log into Windows Live. You then need to (b1) log in using a social account that has the same e-mail address for you, or (b2) log in using a social account that doesn't provide an e-mail to us. In the case of (b2), we'll then prompt you for an e-mail address, and you provide the same one you use to log into Windows Live. That's how we link your profile to the new social account.
Social accounts that fall into the (b2) category include BlogSpot.com, Twitter, and LiveJournal.
We very much want to get Windows Live working again. We're working on it, and you can contact our admin@ email alias if you think you have any clues for helping.