How good is this camera for shaky footage?...because i've seen that the cmos sensors aren't good for this kind of things, but, since this isn't a camcorder, and it also works with dual digic 4 processors, it maybe could hold more the "jelly" thing effect, so, what's your experience with this one?

It's great for shaky footage.

Rolling shutter effect "aka jellycam" is still there at 24p. 60p it's not as noticeable. I just work around it.

Focus on 0:17 seconds, see if you can live with it:
Rails on Vimeo

It's got the same problems as the rest of the CMOS camera world and I believe they can be more drastic in the right situations as well (i.e. really long lens enhances the rolling shutter artifacts). Do some reading and searching in this forum and you'll find discussions and real-world examples of the problem. Even with the limitations the 7D is worth it for what I need it for - and I couldn't use a larger camera as a substitute in those situations. I live with it and it doesn't bite me too often as I know it's there and plan around it when possible.

To the jello-trained eye, no this camera is not good for shaky footage. What you can do is subtly move the camera for depth change, then bring the footage into After Effects and tie a null to a camera and animate the position of the null with a wiggle expression. You can tie the wiggle amount to a slider to control or animate the amount of shake over time. Since you are moving the footage in post (pan and scan) change the shutter angle of the AE camera to have more motion blur. You can also apply a filter for motion blur called "forced motion blur."

All this to say... 7D + shaky footage = best in post

I wouldn't think of shooting hand held with this cam without a lens with image stabilization. If you want your footage to be intentionally shaky, then this is not the cam for you. It'll look terrible.

Now i don't want to make a shaky filming on purpose, but i normally film things handheld, and i also like doing long shots, like a kind of documentary, but do you think that if I add a tripod, or a cheap steadicam, something that gives more weight and more stabilization, will this help the 7D have less 'jello'??...

"but do you think that if I add a tripod, or a cheap steadicam, something that gives more weight and more stabilization, will this help the 7D have less 'jello'??.."

A tripod will eliminate all the jello in a locked down shot. You still may get a rolling shutter shutter effect on fast moving objects but that can be eliminated with the Foundry's rolling shutter plug for AE ($500). It should eliminate most of the jello in a steadicam shot - it just depends on the movement in the shot and how good the steadicam operator is.

As an example (and potentially a shameless plug?) here's my latest work with the 7D. There's one shot in there that has some jello, but not enough to worry about - I didn't and I knew it was there.

There IS, however, a lot of the rolling shutter issues from flash photography - this type of event is a nightmare for the CMOS-based cameras, whether 5D, 7D, T2i, or EX1/3. However, most people don't notice unless you know what to look for. In fact, Fox News was shooting the same event on some big-ass ENG cameras and when I saw their piece (typical news "coverage" stuff) it also had the rolling shutter from the flash thing. Clearly not enough to worry about, and you can cover it up in post if you really want to.

Wilhelmina Brown Austin Launch on Vimeo