My 1Ds 3 is about four years old and still doing great service. Our 5D mk2 is also a good camera, which I really want to like, but it has handling drawbacks. However having looked at the new 5D specs I would say it would now make more sense if I need to upgrade to go to this camera rather than the new 1Dx. The new camera addresses the things I like in the 1 series. Improved viewfinder, better autofocus, dual card slots, and the 'silent mode'. These were all reasons for me to stick with the heavier camera. With an added grip when needed, the new 5D will completely fulfil my personal requirements. More MP may be nice, but in all honesty I do not really need it very often, and most of the time just fills up drive storage unnecessarily. The new features as listed easily make the camera worth more than the Mk2, because it is still going to be significantly cheaper than the new 1Dx.
To all those people who bang on about jumping to Nikon because of extra pixels, presumably they don't have a whole cupboard of Canon lenses. In any case, how long do you think it will be before Canon produces a higher pixel count camera? And just in case anyone thinks I'm an anti-Nikon Canon fanboy, I'm not. I just have invested heavily in the Canon system since my first D30 (the 3mp one) and it is a system that works perfectly. If Nikon had an affordable body in 2001 I would have gone the Nikon route because I had a drawer full of Nikon MF lenses. It shows the maturity of digital that camera systems are not going to be leap-frogging each other in such a big way as they used to. Image quality is the key thing, and that is going to improve only very incrementally from now on.