Many a times you wanted to have your 2 Hotmail accounts window opened at the same time in your browser but you can’t as it would not allow you to do so. You had to logout of one and again sign-in to other. But now with Internet Explorer 8, its possible.
After signing into one Hotmail account, Just click the New Session option on the File menu, and a new browser window will open, and this will not share cookies with the original browser window. So now you can sign-in to other Hotmail (and most other Web applications such as Twitter etc.) as a different user.
If you don’t see your Menu bar in IE8, you can right click on empty space near the tab and tick Menu Bar. Else you can use the keyboard shortcut, Alt+F, I, Enter to invoke a new session.
Here you can see, I have signed into my 2 different Webmail accounts at the same time.
For more Technical details regarding this option in IE8 check IEBlog.