Yep, he's doing it: Billionaire investor Carl Icahn has elected to move ahead with plans to run a dissident board slate at Yahoo, sources familiar with the matter told Reuters on Wednesday.

It turns out Icahn has already lined up 12 potential board candidates to replace the ones that were responsible, along with Yahoo CEO Jerry Yang, for failing to seal a deal with Microsoft Corporation. In a letter to Yahoo, Icahn wrote:

"It is clear to me that the board of directors of Yahoo has acted irrationally and lost the faith of shareholders and Microsoft. It is quite obvious that Microsoft's bid of $33 per share is a superior alternative to Yahoo's prospects on a standalone basis. I am perplexed by the board's actions." CNET News has the full letter.