Yahoo’s official explanation for the changes at the top is being channeled through three directions: Jerry Yang’s Yodel Anecdotal post, the press release and the investors’ call. From the release:

Organization:

—Decker will assume leadership of Yahoo’s business operations, which include the Advertiser and Publisher Group along with the Yahoo! Network, Connected Life, and our International operations.

—Yang will have the Technology Group as well as all corporate functions.

—co-founder David Filo will oversee the company’s technology organization as Yahoo searches for a new CTO.

Semel:

—No separation agreement since he’s not leaving. (Not sure if compensation package will change.)
(See update below.)

—He will serve as “an adviser and important resource for the company’s senior management team, while also working closely with the board.”

The press release has two attachments—a letter from Semel to the board and one from director Ed Kozel to Semel on behalf of the board. Lots of mutual back-patting.

Update: The company confirmed Semel’s compensation status for me this evening. As noted above, Semel, one of the highest-compensated CEOs of any public company, isn’t leaving Yahoo completely, hence no separation agreement. But he is no longer an employee of the company so no salary, no benefits. (The options that haven’t vested already won’t.) However, he will be compensated as a director, which was not the case when he was an employee. Yahoo pays $15,000-$35,000 to the chairs of various committees and reimburses some expenses but the bulk of compensation for non-employee directors is in the form of stock options.