I've been testing this for a while now and hadn't noticed it had gone public beta. Live Mail Desktop is like Outlook Express on steroids with a cool UI and integrated junk and phishing filters plus RSS feed reader. That's at least 4 RSS readers I have on my PC now :)
I'm using Outlook 2007 for my mail in the main and RSS feeds but if you use Hotmail this is a pretty cool application that I'd recommend checking out for taking email offline. It even has a built in blogging feature and Active Search which looks like a cross between Instant Search in Outlook 2007 and Live.com search.
Full details on how to sign up at the link below
Link to Windows Live Mail Desktop Beta: Our Beta is public!