If this report is accurate, at least someone outside the core production team knows that's happening in Episode 13. According to a few sites, citing writer John Fay's website, the co-writer of Torchwood: Children of Earth is currently writing an episode of Doctor Who.
http://news.whoviannet.co.uk/2011/06/john-fay-writing-for-series-7-of-doctor-who/
Of course there's nothing saying such an episode will see the light of day (paging Stephen Fry) or if it'll air in Series 7 (paging Neil Gaiman), but the fact a franchise-connected writer is doing an episode (and he wouldn't put it on his CV if it wasn't serious work) is being touted as the first direct indication that, yes, Virginia, there is a Series 7. (There's been some fear and loathing over the fact the BBC has yet to officially commission it, even though the odds of the BBC not renewing Doctor Who are pretty slim. Mind you, John Nathan-Turner had commissioned a full slate of Season 27 stories too, and we know how well that worked out.
)
Alex
http://news.whoviannet.co.uk/2011/06/john-fay-writing-for-series-7-of-doctor-who/
Of course there's nothing saying such an episode will see the light of day (paging Stephen Fry) or if it'll air in Series 7 (paging Neil Gaiman), but the fact a franchise-connected writer is doing an episode (and he wouldn't put it on his CV if it wasn't serious work) is being touted as the first direct indication that, yes, Virginia, there is a Series 7. (There's been some fear and loathing over the fact the BBC has yet to officially commission it, even though the odds of the BBC not renewing Doctor Who are pretty slim. Mind you, John Nathan-Turner had commissioned a full slate of Season 27 stories too, and we know how well that worked out.

Alex