I think it is important to have a free site and to keep ShareCG free. It has developed a brand on this name within the graphics community that should be leveraged, not changed.

Two things I notice right away from their model. First, there's not much traffic at this Forum. If I posted at Daz there would be hundreds to a thousand views on a subject like this. Even Renderosity, which doesn't have as strong a set of Forums, would have more to say on a subject like this. 

Actually there IS a thread dedicated to this topic at Daz which has over 4,000 views:

http://www.daz3d.com/forums/viewthread/8486/

You should be able to build a forum on a free site such as this and have more stickiness. And a free site such as this should in theory be probabaly the least biased towards having discussions about all the other companies who pay to have products out there. How does eHow or other sites make their revenue?  Wikipedia?

Second, the ads are generic. While I'm here I'm more likely to click on an ad that talks about other 3d items, other 3d sites, 3d magazines, other graphics programs, reviews on graphics equipment, from monitors to motherboards, gaming, etc. you get the idea.

Third, people grow. I can see where beginners look to post to the widest possible audience first and then later get to a point where they think, 'maybe I can sell some of these items.'  If you're going to make it 'pay' think about expanding and make a sister organization separate from share CG where ther poster gets some share of what is put up. The thing is, then you're going to have to have some sort of support organization to monitor the quality control and eventually generate excitement.

I think there is still a lot of opportunity here.

That's all I've got for right now.

Be well.

"If Life gives you melons, maybe you are dyslexsic; If life gives you Lemons, keep them. Hey, FREE Lemons!" (Snorg T-Shirts; See -  I do click on some of the ads!).