I'm running a few days old WebKit nightly by the way (in my OWB build).
The thing is hotmail doesn't support many browsers, and forcing OWB user-agent to firefox or safari helps with these buttons, which at least act when clicked.
Unfortunately, there's still an issue when clicking a mail or performing most actions: hotmail complains it can't connect to windows live messenger. So I guess it might be some other cookie issue. Not sure yet. :)
