Sorry for not jumping in here sooner, I took a couple days off to deal with a few things.
On Participation: I think the ideas presented so far are all good tactics. Getting the challenges out there each week always helps, as does promoting a general awareness that we're here. I've done what I can to do my part, but like myself a lot of the core group right now tends to mostly reside in this section of the forums. Those who do travel around should definitely spread the word as best they can. The mentoring thread should also generate some visibility. The trick really is to get one or two heavy hitters involved on a regular basis. People often flock to where the talent is. Another idea to throw out there would be every so often to have a week where we tie into the CHOW topic. For example with the current one, some sort of religious object would be appropriate. Then those working on their CHOW entries could think about the IDW one in parallel and see if they want to work on both entries since they're in the same line of thought. I say CHOW because it's the most relevant to ID, whereas objects for creatures or environments would be harder to fit in closely. A character always has accessories though. Just one idea.
On References: I'm actually of a different mindset than most on this one. I feel slamming too many references of other people's work can often influence one's design more than it should. There's a fine balance somewhere in there that should be held. Additionally, I think it goes against the spirit of what we do here. One of the core ideas behind following weekly briefs is to emulate a working environment, where you're given a topic and you have to deliver. Collecting references is a big part of what a designer has to do when working on a project, and I think it's important that each one goes through that on their own as opposed to being handed everything on a silver platter. A few references for inspiration are fine as part of the brief and often are present at work as well. But I've seen some rounds that were utterly swamped with reference material. Call me a strict and mean bastard, but pushing ourselves is what we're about and I feel that's part of the process. Now a separate thread where we might share inspiration that's unrelated to a topic is a whole different matter, and would likely help many. But that should serve as general inspiration. If we're doing tanks, that thread shouldn't be flooded with tank images for the week (and why the hell are we all using tanks as an example, heh).
On Critiques: As any regular participant as of late knows, I'm big on them. For me it's as important as the creation of an entry, because one often learns as much from both. I've said this before, but I think crit for those who participate in a round should be mandatory. If you spent a week working on and submitting an entry, you should be able to find a few minutes to offer in-depth critique for everyone else. Especially since you'll be receiving critique on your own entry from others. For those that didn't participate it should obviously be optional and welcome, but for participants it should be at least an unwritten rule.
All for now as I have to get back to work.
PS: Yoitisi, I'm all over the icon situation and I'll shoot some ideas to you soon. I actually started working on this a while back after talking with Oregano about their icon plans for CHOW, which he told me he'd touch base with you about. I'm guessing he recently did and that's why you brought it up.