Awesome a camera as the 5DmkII is, two main problems come from converting the the CMOS sensor image from stills to video are; Moire and Aliasing. Moire is the 'rainbow effect' when shooting video of fine detailed surfaces like certain rug and clothing patterns, brick walls, etc. Aliasing is those lovely jagged edges in the images when they should be smooth.
However, there's a solid fix for that now with the Mosaic Engineering Optical Anti-Aliasing Filter. Here's a vid by cinematographer Glenn Przyborski giving a rundown on what the filter can do in the MkII.