I just noticed it today, while logging on to MSDN subscriber downloads. The Passport service, which is the main identity system for Microsoft's web sites, is using a new domain name. We are now redirected to https://login.live.com instead of the old https://www.passport.net. This is part of the move of many Microsoft web-based properties to the new, comprehensive Windows Live brand.
Although the web page at http://login.live.com still show the Passport brand, this is expected to be renamed completely to Windows Live ID, which is already mentioned on the page as well. I guess this was done this way to ease the transition and avoid user confusion.
To see more Windows Live services, check http://ideas.live.com. Most of the new services are still in beta.