I'm not one for rumours, but across last year various things have been said by people who may know something including interview information printed in; Out Northwest, DWM, The Telegraph, The Writers Tale, Doctor Who Advent Calendar, BBC, SFX, Doctor Who Forum, News of the World, Daily Star, Radio Times, DVD commentaries, Podcasts, The Times, Outpost Skaro, Sunday Express, and many others (appologies if I missed you).
These are all unconfirmed, but more likely than some of the rubbish you read!
Filming of the specials is confirmed to start on 19th January 2009, it will continue until May, editing etc. in June-August, then season 5 filming will start! David Tennant is already back rehearsing with Hamlet after his operation, so hopefully no delays :)
The First special Planet of the Dead, is at Easter, then there may be nothing on our screens until Christmas, which will have a stand alone story on Christmas Day, then a two parter where Tennant becomes Matt Smith over new year. They have two huge Guest Stars for these. The last special will lead into season 5 with a cliffhanger, instead of ending a-la-the Stolen Earth.
The last three stories are supposed to feature Donna Noble and Wilf, with Captain Jack in the last two and into season 5.
All specials will be one hour long, and will not be made in HD, they are to be filmed in the USA and Egypt, and Dubai has been mentioned too.
Some of Planet of the Dead will be filmed in Tunisia, a big-name female is promised.
One companion in the specials will be in her 50s.
We may see the TARDIS control room is redesigned.
A Sea Devils story looks like a definite, and it may feature the Brigadier & UNIT too!
Winston Churchill is rumoured to be in a story.
One story will feature a humanoid alien who can suck peoples emotions/thoughts out of their heads.
The Master is to return, probably with Harriet Jones (who we never saw die remember), she has been in league with him since before The Stolen Earth, the Master didn't want reality to be destroyed either!
Patrick Stewart may appear as the Meddling Monk.
Zygons and Ice Warriors are monsters talked about appearing.
You may have heard versions of these, or differant rumours, I have tracked these to internet source! Even ones that are correct at time of printing are subject to change! Whatever happens, they are going to be great stories!