I really dig the simplicity of the process. I love that the entire top of the homepage not only shows exactly what you offer, but it is, essentially, your entire user-facing product. The price point is a little high compared to normal custom t-shirt offerings, but if you're offering higher quality shirts and a better user experience, then that isn't a bad thing.

A couple of suggestions:

1. The person/model used for the primary image/ordering system looks miserable. "Look, you can get your own custom shirt, but it isn't going to make you happy" doesn't exactly seem like the message you're trying to send here! A smile would go a really long way. Also, the cropping around the hair makes it look a little less professional. I'm not a designer, and I'm sure it is difficult to get something like that perfect, but I think it is worth the effort given how prominent the photo is.

2. The photos of the t-shirts themselves make the t-shirts look like they're low quality (specifically, really thin). I'm not a huge fan of white shirts in general, but I definitely don't want any t-shirt that I can actively see through. Sure, your "gallery" model may be attractive, but it doesn't look very professional (nor does it speak highly of your shirts) if you can see her bra through the product.

3. I feel like the "About, delivery & more" link should really link to the "About" section. I was a little confused when it jumped down the page and I was just staring at some random "suggestions" which, in my case, were not interesting. There's nothing wrong with the suggestions, I just don't think they should be more prominent than "About".

4. I'm on a 27" thunderbolt display, and the marketing material in your bottom tabs is taking up less than half of the bottom of my screen when I am scrolled down as far as I can go. That's not the worst thing in the world, but I would rather scroll down than just change the bottom 40% of my screen when I click "tabs".

5. I'd want more information about the product, the company, and possibly you before I order anything. If you're trying to sell quality, then a full page talking about how damn awesome your shirts are would go a long way to converting me to a customer. And after you sold me on the product itself, I still wouldn't feel safe ordering anything from an unestablished company with no business address, almost no information about the people behind it, and no contact means other than email/twitter.

All in all though, it is cool to see what you can accomplish in only four days. Best of luck.