As someone that has multiple hotmail/passport/live.com accounts, I think this is really really cool!

Do you have multiple Windows Live IDs? Maybe an older one and a new one, one for work & one for home? A public one and a private one? If so, you know that in the past it has been difficult to manage and switch between your different identities. No more! Windows Live now offers a Linked Windows Live ID service. This service lets you link your Windows Live accounts together and easily switch between them.

Link Your Live IDs Together! | Sarah In Tampa | Channel 10