Hey, it's doing this because of a bug in either Hotmail/MS Passport's authentication system or Safari's handling of said authentication. Regardless, you've got automatic login enabled, right? Just turn that off. I think if you get rid of the cookie you should be fine. Of course, you could always go to MacUpdate & download the httpmail plugin (
http://www.macupdate.com/info.php/id/10842) to read your Hotmail in Mail.app.
That's what I do.