This one is neat, at least for me, as I do maintain two different Windows Live IDs (one @hotmail.com address, that I'd like to deemphasize over time, and one @live.com address that I'd like to use regularly once Microsoft starts handing out live.com addresses to the public). Anyway, this is a great idea though I'll need to test it more to see how it works. I hope they add this capability to their Windows applications, too. For example, I'd like to switch between IDs in Windows Live Messenger or, better yet, have them both active simultaneously.

Got multiple Windows Live accounts?  Sick and tired of having to log out and back in again to switch between them?  Well, no more!  You can now link your Windows Live IDs together so you can switch identities in one click from the menu on the top right of most Windows Live pages.  

To set this up, go to https://account.live.com and look for the section called Linked Windows Live IDs.  There's a link there to manage your linked IDs.

Once you have this done, Sign Out, and then Sign In Again.  When you go to sites like Windows Live Spaces and Windows Live Events, you can click on the top-right of the Windows Live header bar (click on the down arrow next to your name) and you'll be able to instantly switch to any of your linked IDs.

This is a really cool feature that took coordination from a lot of teams to get done.  I'm thrilled to see the last piece ship so that users can now take advantage of this.