This rumour is nearly there, but misses a few of the basic rules of made-up rumours; here's my take on how to make one up:
Canon 5D MkIII to be announced early 2011
28MP -new breakthrough in S/N for Canon
1920Ã—1080 30/25/24 frame Video with manual audio levels, peaking and zebras
3:2 aspect ratio tilt/swivel screen
63 segment iFCL meter
Same AF as the 5D MkII -Canon believe that most users were satisfied with AF performance
+ a new feature for Canon EOS cameras
First, you must keep the date vague for a bit of longevity -if you give an exact date that is only weeks away you'll be quickly disproved.
Note how an effective made-up rumour combines the believable (and totally expected) specifications with those that will cause excitement such as the S/N ratio BS (the video stuff that I don't really understand, but is easy to lift from any internet wish list).
The controversial features need to be included: a tilt/swivel screen will split opinion between the 'must have for video' crowd and the 'likely to break and so not professional' elements. I've gone out on a limb with the statement that it will keep the 5D MkII's AF system; most people would find it incredulous that Canon would keep the most critisied feature of the MkII. Then again we've been shafted by Canon on so many previous occasions that the seed of disappointment will already be in their minds.
Finally, you need to give a mystery feature -this both invites speculation as well as covering you against major new features that you missed.