I'm curious. What does this mean exactly?
I'll preface this by saying that I'm probably looking at it from a more idealistic standpoint than a practical standpoint. That is, I care more about what this
means than what it functionally does or will do.
But if WotC gets ownership of everything you post to Gleemax, that means they can do with it whatever they might want to do at the time, and you have no say in it whatsoever. At least, legally speaking (I'm sure at least the first few people they want to use will be contacted about it).
Which means, fundamentally, that you don't control what you put onto Gleemax. That they are totally free and clear to do anything with those posts. This includes publishing them without your consent, but also includes selling them to other parties, using them in advertising, etc.
Say there is a Gleemax "post pictures of your gaming group!" thread. Those pictures then become property of WotC. Any drawings of your characters become property of WotC. Any pictures you find on the internet of other peoples' drawings and post to Gleemax as a representative of your character (say you found something cool on Conceptart.org) become property of WotC (which is part of how this gets legally sticky and ends up getting fans sued). Then they use a photoshopped picture of your wife as the Whore-Demon Bthalbir, they use your drawing of a nude elf (posted because you were doing a body study of the different races) to mock the Book of Elf Porn, they sell the Conceptart.org picture to the studio doing the next D&D movie and get everyone sued because of a fan's use of a picture....
They OWN what you post there. You don't. You don't control that information anymore, they do. That's much more than just trusting them. That's giving them a little present every time you 1's and 0's it up over there. And just like you can't control if someone you gave a golden ring to melts it down to pimp their smile, you can't control if that little YouTube you posted involving your gaming session gets used as the next D&D commercial.
I'm pretty sure WotC is a stand-up company, but they already get my money, I'm not going to give them my words, my thoughts, my drawings, my pictures, my accounts of my life...