I'm a producer, and own a clip store, so I'll qualify my remark by making that point.
That being said, I still think it would make sense to have a separate "preview clips" forum from what would amount to a "real" clips forum - that way, the advertising for C4S previews could be separated from "real" clips (home-made, not-for-sale, etc.) material. I don't even post video clip previews that often in the vid clip thread anymore - the second I even do, I get leap-frogged by 83 other "ZOMG BEST CLIP EVER" threads from everyone else. I was posting a lot more previews initially, and realized I was just contributing to cluttering up that section of the forum. Now, when I do post, it's links to multiple previews, and far less often...and I keep my preview/announcements limited to screen cap posts in the image forum, and a continuous update thread in the C4S section. People can find my stuff if they want - I don't really think posting 20 preview clips a day is going to necessarily drive traffic to my store. And again, I do think the advertising/previews should be separate from true "real" stuff - that way, people who aren't interested in buying clips can find the other content more easily.