A wedding is the most common of the happy endings in movies, theater plays and also in the stock market.
A wedding of Microsoft and Yahoo would make very happy to Yahoo investors (specially those who bought in the last months), trading banks and stock brokers that will cash nice fees.
But what about the end-users? Why should we be happy with one option less for webmail, for instant messaging, for on-line video, for on-line pictures, and specially for on-line advertisement?
As a user, I always prefer to have three options than two. It is called competition, and it is what drives innovation, better service and better value. Oligopolies are not good for customers.
Stock market and investors love mergers and acquisitions. They make the market more active with bigger transaction (and fee) volumes. And above all it pleases investors, because a player in a market with two players is more valuable than a player in a market of four. In other words, business owners love oligopolies. Microsoft is the living evidence that a near-monopoly in the PC OS market brings huge returns.
Beware, because a Microsoft-Yahoo wedding will be a happy ending only for a few investors and bankers, but not at all for the majority of us.