From Microsoft:

Today, Microsoft announced that Hotmail email account aggregation is rolling out in the US, Canada and Brazil.  This is a feature that allows consumers to receive email from other POP-enabled email accounts (including Gmail, Yahoo! Mail and AOL) directly into their Windows Live Hotmail inbox. With this new feature, Windows Live Hotmail offers a one-stop place for managing email, making it easier for more than 400 million Windows Live customers worldwide to manage their multiple accounts from a single location.

For more info, check out the Windows Live Wire blog.