As noted previously, Microsoft planned to close WebDAV access to Hotmail in June 2008. However due to customer demand, they changed their minds. Since then they've implemented POP3 access for Hotmail, and because of that, have decided to fully close down WebDAV access on 1 Sep 2009.
What this means for FastMail users is that if you're using a Options -> Pop Link to download Hotmail email to your account that's a Hotmail type link, you have to change it to a POP type link with the following details before 1 Sep 2009.
You can use the Test button lower down the page to confirm that your new settings are working correctly.