From a still photographer perspective, moving to motion, there are some things you see in motion, that will never bother you in stills (like hand held), some things you see in stills that just don't resonate that much in motion, (like slight change of focus as a subject moves), but the most glaring issue of the dslrs used for motion is pattern moire.
This is a small crop from a project last week, shot in vertical motion.
In a still in can be corrected, (not easily, but not break the bank hard), but with motion it's glaring because you can see the pattern moire move. A dslr with motion (5d2) reminds me of shooting a 6mpx still camera. You have to check for this type of artifact or moire all the time and it's impossible to see it on the back of the camera, even difficult on a 7" hd monitor with hdmi connection.
Luckily we caught it early, changed camera position and moved on, but had we not been aware of it this would have been a deal breaker.
It is also very important that you treat motion with the same respect, (sometimes even more) with your workflow. All too often still photographers are placed in a position to shoot motion as a secondary part of the project, which translates to less time for workflow, checks, calibration, even proper production values and it's kind of a fright because we can be exposed to this type of issue which can be a costly fix in post.
In certain ways, I think the 5d2 is an amazing camera because it works so well in low light, it's form factor is small enough, even with all the gizmos attached to move quickly, but other things like these artifacts, the in ability to really mark focus points and some of the other workarounds make the RED look more like a solution than a web movie overkill.
Though once you get a 5d2 with everything it takes to work professionally, it becomes a rather large camera and in this case the tripod you see here is not large enough, (we only use this manfroto to shoot low angles where we can spread the legs and even then you have to be extremely careful to keep it smooth and steady.