The deal is expected this week! It appears that the poor quarterly earning pushed both sides to get it done.
At the time of the launch of Bing, Steve Ballmer had indicated that he was willing to invest 5-10% of Microsoft's operating income on search within the next five years.
The 5-10% of operating income translating into $5.5 -$11 billion would give us the size of the transaction deal. Additionally the investment to be made over a five year period would corroborate the indications that Yahoo may not get a huge upfront payment and it would be a revenue sharing deal.
As for the transaction value, Microsoft would not only consider the revenue impact to Yahoo, it would also consider the savings to operational costs for Yahoo.
Carol Bartz on the other hand would be looking for boat loads of cash.