I am a UX guy who specializes in community design, and I see some fundamental areas you should work on:
1.) How is this better than Dribbble; a popular, well-respected site with precisely the same pitch? That's not a criticism so much as something to think about.
2.) You forgot half of your target audience. Community like this has two user types that support each other: designers and critiquers. Ideally the critiquers are designers too, but these are two separate behaviours, and your site is designed for one of them. You're never going to reach critical mass until you cater more to the majority (non-uploading, non-commenting lurkers).
3.) It's hard to browse. The start page has a few clickable images and once you choose one, you're doomed if it wasn't something you like. I bet the exit rate (Google Analytics) on that second page is through the roof... what should I do next if I didn't like it? Hit the back button? That's a no-no.
4.) The users are too downplayed. In a community like this, people discover the users through their content. Then they want to follow and see more, which motivates registrations. You should make it obvious who has posted each design, with a clear link to see more.
5.) You did a good job of selling the concept on the start page, and the path to registration is obvious and clear, but I don't want to sign up for something as time-consuming as a community without trying it and exploring a bit first. That's the part that isn't so great right now.
6.) I don't get the metaphor. Is it military or something?
7.) On a purely aesthetic level, you might consider simplifying your brand... there are a lot of colors, and mid-tones, and textures, and geometry, and it's forcing you to use lots of boxes and stuff. It's hard on the eyes. Pick a couple colors, a motif/pattern or two, and reduce, re-use, and recycle. ;)
Good Luck! Nice effort so far!