Microsoft + Yahoo = ?

Microsoft planning to buy Yahoo for $44.6 billion. Until now Yahoo hasn’t give final answer it.
I’m wondering why do Microsoft want to buy Yahoo, is it for fighting Google?
Or Microsoft just want to kill one of hisĀ  rival.

Let’s see
IM : Microsoft has Windows Live Messenger, Yahoo has Yahoo Messenger.
Search Engine : Microsoft has Live Search, Yahoo has it’s own search engine.
Email : Microsoft has Windows Live Hotmail, Yahoo has Yahoo Mail.

Let’s wait for Yahoo’s final answer.
And how will Google respond about this :)