I'm looking at numerous videos shot on 7D at 3200 ISO on Vimeo, and the noise doesn't look too noticable at all to me. Then I look at my raw footage from my camera at 3200 ISO and it is very noisy

What factors effect the amount of noise in the image, other than the ISO, is there some trick all these people are using to limit the noise at this ISO?

most likely it's the compression used for web. That can reduce how noticeable the noise is. Could also be using a noise remover program such as neat video or foundry plugin

Probably the latter. I always run my high ISO shots through noise reduction. It really works pretty good unless you are in the extreme range.

Of course extreme is relative in these new cameras ;)

Neat Video is absolutely worth investing in if you plan on doing a lot of high ISO shooting. It can really save the footage.

How does the in camera high ISO noise reduction fare? I tried it out awhile back in a dim light venue at 3200 and 6400 and footage seemed to come out OK.

During a presentation at NAB, Vincent Laforet mentioned that he used Neat Video on Nocturne.

'Nuff said.