TrekMovie.com says they've confirmed all of these with multiple sources; obviously, take them with a grain of salt, but I don't recall TrekMovie.com getting much if anything wrong, so I'm inclined to believe these are true.
• Leonard Nimoy is returning as Original Recipe Spock.
This sucks, in my opinion, because 1) they already did it in the first movie, and 2) I'm quite ready for the new Trek-verse to stand on its own. Plus, I don't think there's going to be a good reason for him to show up other than to remind hardcore Trek fans that yes, the original Trek is still out there, somewhere.
• Benedict Cumberbatch is playing Khan.
We all suspected this, but it's disappointing it's true. Avoiding the whole "casting an originally ethnic role with the whitest, most British British man to ever have lived" kerfluffle, again, I want the new Trek movies to stand on their own, not just do a rehash of original Trek's greatest hits.
• The Klingons will be in the movie.
This is the one bit of news I'm not disappointed by. I was really hoping the Klingons would be the baddies of Trek 2, if only because they haven't been real Trek villains in forever. It would have been neat to see them as the antagonists again -- and certainly, you could tell some new/original stories with them if you were so inclined. Khan is just so specific a character that even if you try something new, we'll all just be comparing it to the original Star Trek 2.