Here's my opinion on what's going on:
People think the 5D2 has less noise - I think the signal to noise ratio of the sensors is probably about the same, maybe the 7D has a small lead because it's a next generation sensor with more readouts and "Gapless MicroLenses." I think the 5D2 has less PERCEIVED noise in the video because the debayering algorithm, combined with Canon's Noise Reduction, combined with H.264 encoding obliterates detail.
Sorry to break it to you folks thinking the 5D2 has any sort of lead (besides sensor size) just to give you an idea, use the focus assist on a 5D2 and a 7D side by side - you will immediately notice more "noise" or buzz in the magnified image. Not only is this an enlarged portion of the sensor readout - it also doesn't appear to be going through the noise reduction algorithm. This is what the sensor is actually seeing (sort of).
The 7D is using a different algorithm, and because it is actually resolving more detail it is also resolving more perceived noise. By resolving, I mean what the backend recording part of the camera is receiving from the sensor. Personally I think this is a good thing. Just compare any large smoothe surface in a 5D2 video next to a 7D video and you should be able to see what I mean about the way detail is handled. On the 5D2 many things with detail (including human skin tones) are sometimes reduced to a watercoloury gourade style shading. The 7D smoothes less at a pixel level, which shows more perceived noise/detail. If I have time I will do a comparison, but for now I just wanted to get this out.
Now, I'm not knocking either camera here - just making an observation. As a realist I perceive all new cameras as essentially new film stocks.They all react differently to different exposure, and they all have intricate qualities of their own. Like film stocks, they have strengths and weaknesses. We as camera people just have to find the strengths, and work around the weaknesses to get the best results for whatever we shoot.