If you consider casting news to be spoilers, then you might want to avert you eyes. At this point the cast is about all we know, but it does provide some interesting information.
What we do know leads us to a gathering of three doctors. Our current 11th Doctor, of course, his predecessor, the 10th Doctor (David Tennent is back), and a future Doctor. There is no indication whether John Hurt is playing and old 11th (doubtful), the 12th, or the 13th incarnation. Just that he is the Doctor. It is the first time they have looked into the future like that.
That, plus the casting news the Matt Smith and Jenna-Louise Coleman will be back for an 8th season, means that we won't be seeing a regeneration or anything happening to Clara.
We also know that Rose is back, as is Kate Stewart. IMDB gives a few more cast members in roles that either are yet known or that don't mean much.
There are no hints of the plot as of yet. While I am more than willing to divulge a great many spoilers, Doctor who is a show with a lot of mystery and maintaining that is a good thing. I won't be looking for or sharing the great secrets of the plot, only the initial setup.
One cool thing I found was the following video:
Most of the rest of what I have heard are rumors. Some say that John Hurt's Doctor isn't a future one, but a past one. The rumored antagonists include the Zygons and Omega. And Queen Elizabeth I may make an appearance. But I can't trace any of these back to a source of any repute. So I will wait and see. More will follow as I know more.
One of the more interesting setting tidbits is that we might be revisiting Coal Hill School and Totter's Lane. It remains to be seen if this is actually connected to the 50th Anniversary Special or if it is a false link from sets used for An Adventure in Space and Time. In any case, it looks like Moffet has a wild ride in store for us.