Feds raided Jason Grimsley's home looking for evidence that he distributed HGH. Grimsley (or "Grimey", as he likes to be called) then cooperated with authorities, for a while. There's now a huge affidavit (available here), where it's clear he started talking. Among other things, he named names of other MLB players he thought were using (the names have been redacted, though word size may offer clues), so this investigation is just beginning - it could get real ugly.
(It's worth mentioning that this disclosure comes just days after a pretty good article (with a great title) by Jeff Pearlman, about the naivete associated with the "Post-Steroid Era". A lot of people got super-defensive about it, as they felt it implied that Pujols was a user. But if you actually read the article, you find it does no such thing - it's about the sportswriters.)