So what is the actual defining factor, if you are judging this based on "serious investment from Microsoft bid"?

Since they've rejected the original bid, does this mean Microsoft has to make another bid, which Yahoo then accepts? Or does this mean that Yahoo will change their mind, and accept the bid after all by mid-March?

I don't really feel comfortable making a prediction bet on this until it has been clarified as to how this is going to be judged.