Just because I already own one. Been using it for years since it came out, and are quite satisfied with it. Just thought that because they promised an APS-C anti-moire filter, I wonder if they'd fulfill their promise. Ah, well.
I don't see the point in sidegrading to a 5DMkII other than the full frame. Still had to deal with softness/jello/moire.
Thought of upgrading to 5DMkIII, but the benefits for video seems minimal. I'd rather get a GH2, but I'd have to get some panasonic lenses (mostly kit lenses, but eh) and a metabones adapter for the canon glasses I have, but that adapter costs almost as much as a GH2, plus import tax.
NEX7 is just as bad for video, if not worse due to the codec.
I don't use my camera professionally anyway. Looking forward to the 650D with the rumored AF during video, but canon would probably screw it up anyway, like they did with the 5DMkIII.