As informed by IGN, id Software's JC, John Carmack, decided to leave the company.
"John Carmack, who has become interested in focusing on things other than game development at id, has resigned from the studio. John's work on id Tech 5 and the technology for the current development work at id is complete, and his departure will not affect any current projects. We are fortunate to have a brilliant group of programmers at id who worked with John and will carry on id's tradition of making great games with cutting-edge technology. As colleagues of John for many years, we wish him well".
- Tim Willits, Studio Director, id Software

"I wanted to remain a technical adviser for Id, but it just didn't work out.
Probably for the best, as the divided focus was challenging."
- John Carmack, @ID_AA_Carmack

Source: IGN, Carmack's Twitter
News: kotaku, eurogamer, shacknews, bluesnews