Clara...

..or shall we say, who is "Clara Oswin Oswald"?

Moffat actually gives us more clues than we think, you just have to find them.  But the clues really don't help...that is the problem.  The more clues, the more the puzzle deepens.  (Just watch "The Pandorica Opens" and try to wrap your head around that one!)

Clara was born November 23, 1866 and died December 24, 1892.  The year may be insignificant (or not), but the date "November 23" is quite significant.

There can be a loose theory that this somehow ties in with the first episode of Doctor Who airing November 23, 1963, but I'd rather believe...

...that the Silver Nemesis is returning.  It last appeared in 1988 and returns every 25 years...which means it comes back in 2013.  The Silver Nemesis is made of Validium, so it cannot be destroyed.  When it dies, it just comes back as another form.  The Doctor has been battling it every 25 years (as I understand) since like 1638.  So....is the Silver Nemesis actually Clara Oswald?  ...is that why she says "run you clever boy, and remember me"?

Hmmm?