This last week Microsoft released the Windows Liver ID Authentication SDK so that you can now authenticate users by their Windows Live ID (passport revisited).  I was wondering just how easy/hard it will be to use and found that from that looks of it, the system is simple to get up and running.  Here is the post on Dan Wahlin's blog that makes it quick work:

http://weblogs.asp.net/dwahlin/ archive/2007/08/17/ integrate-windows-live-id-authentication- into-your-website.aspx