First off, I think your concept is brilliant and there's a lot of potential. To me, this is one of those markets that should be targeted at women/moms (see the recent HN post on Ravelry). My wife and her friends were actually just talking about this very need yesterday ... they were looking for ways to put tree/bird designs on their wall.

That being said, here's where I think you can improve the execution:

1. Make the site a bit more feminine. Not really a fan of the blue background. Go something lighter, more neutral, maybe a little feminine. Maybe just white like an Etsy.

2. It's not immediately apparent that you can make and sell your own designs. If you're going for the Cafepress angle, I think you need some more obvious buttons/labels for that. At least make the "make" and "sell" buttons on top stand out better.

3. Add some more social/sharing features. Let women/moms create designs and share them with other users. Maybe you do it already, but let people save their favorite users, designs, etc. Again, look at Etsy for cues here.

4. Add a religious/spiritual category right away. As a Christian, trust me–if you have a category with bible verses and religious quotes, it would be a big seller. It's a huge market and I have tons of friends who would buy such graphics for their home.

5. The home page seems a little busy. I'm not sure what's most important to you, but I'd recommend some A/B testing to see what best improves your conversions.

Anyway, good luck with this. I think it has potential. I already showed my wife and she digs it.