With Microsoft's $47.5 billion (at $33 per share) bid for Yahoo withdrawn, at least for the time being, some people label it as a failure for Steve Ballmer. It might be a failure in the sense that the deal didn't go through, but on the other hand had the deal gone through success wasn't guaranteed. One is probably well-served to remember that most (friendly) major mergers and acquisitions don't create long-term shareholder value.
In order to create value after paying anywhere near $50 billion, a lot of things have to go right. Anyone can decide what the odds of a lot of things going right would be with the actions taken by Yahoo to discourage Microsoft's bid, Yahoo's weakening position in search, the likelihood of having to spin out either Yahoo! Mail or Hotmail and the business operational issues of both Yahoo! and MSN.