Microsoft has given Yahoo until April 26, 2008 to accept their buyout offer or they will launch a hostile takeover and offer less money.
The offer was worth 44.6 billion dollars when it was first announced. It is now worth about 41 billion dollars.
These articles have all the details:
Microsoft Gives Yahoo 3 Weeks For ‘Definitive Agreement’ To Buyout
Microsoft Gives Yahoo Deadline on Offer: Financial News - Yahoo! Finance