Personally, I must disagree. I don't think divx is a scam, and I have nothing against that they try to make money. But I do not consider it a worthwile project anyway.
As they admit themselves, the field of digital video compression is riddled with patents, and divx most likely breaks most of them. As a free software enthusiast, I cannot say that this makes me very interested in contributing to divx or project mayo. There are other more worthwile projects out there that would result in something not only useful, but also something that would be legal to distribute and use.
Secondly, divx is not free software, and it's copyright status is at best uncertain. Again, to make sure it is legal, we will need a clean-room implementation. And, given the legal status of divx, the divx developers are not able to do that, as they are already too much exposed to copyrighted code.
Thirdly, I do not agree with their goals and ideals. Divx was written as a tool for piracy. It breaks patents, most likely copyright, and is primarily being used for breaking copyright. I think it is important for free software to stay on the right side of the law in order to be accepted by the public. And while divx certainly has legal uses, it is my impression that those are not the reason for it's development.
The sad thing is that it might take a long time before we will have something like a good free video codec because there are so few hackers who have intricate knowledge of video-compression. Even less of those would be eligible to do a clean-room implementation of something. And you have to be really smart to get around all of the patents, and still come out with something useful.