Newsarama has an interview up today with Busiek where he discusses his Superman run, and his premature exit from the title. Issue 675 will be his last, which means there are only 3 issues to go. With a storyline still ongoing, we may not get to see that anticipated return of Paragon that he had promised earlier in the year.
It isn't all bad news, however. He's leaving Superman so that he can focus his energies on a top-secret title he's working on with Mark Bagley(artist of Ultimate Spiderman's first 100+ issues), and he has a Superman mini that will be coming out sometime soon, as well. Plus he says he has plenty of stories in mind if he makes it back to Superman after finishing this project.
Oh yeah, and he said earlier that Arrowsmith may be getting a sequel series. So there's a silver lining in there.
If your interested in the whole interview, which is a bit dry, follow the link.