Isn't this kind of funny? IE9 can do IE5, 7, 8, 9 all together. Ironically no IE6. It has the Force mode. Not entirely sure what that mean actually. Anyway, isn't it funny to see how small the download and there is no install stage at all? If there is install stage, obviously it is too fast to notice. And then, there is this ability for you to use IE8 along with IE9.
But, I assume once they RTM, they are going to make is so big and install like super super super slow. And they ironically will force removing IE8 since they like to get crazy.