I know that a lot of people are not interested in the rumours, so I'll not go into any details here.
I started collecting a few notes about them in 2004 (long before the rumour blogs) when I was looking for new equipment myself and confused by all the seemingly random stuff appearing.
In many ways I'd much prefer the site to be better known for the articles and reviews I write, but the visitor numbers the established rumours pages bring in are something that no commercial site can ignore (remember that the site also brings me in new commercial work).
Over the years, the single most reliable timing predictor of Canon's evolutionary design strategies is the EOS DSLR time line and their normal timings for announcements.
The quantity of good solid leaks has declined rapidly, as 'those that do know' are under stricter NDA agreements and have more to lose by saying anything. If you look at some of the stuff that has appeared recently, much is just noise from the 'I want it now!" contingent.
My particular interest here is that my own 1Ds3 is now ~3.5 years old and what comes next may influence my choices as to whether digital MF is of business relevance to my own work (note important distinction from something I'd like to play around with ;-) )BTW - Happy to discuss rumours on Google+ (seems a more appropriate place ;-) ) http://bit.ly/northlight-gplus - I have some spare 'invites' too if anyone wants to try it out.