Front page is really busy. I would tone it down a bit (maybe get rid of featured items or best sellers or something). Red on Black text is hard to read and so is red on blue (product titles). Same with "About" page....you could bold the white text so it is easier to read on the blue background.

Checkout pages

I like how you don't have to log in to your account. I don't know how you got rid of the first page in Miva Merchant but that is cool. Money order/Check print option...great idea!! I'm not a fan of upsale, especially when it doesn't seem to relate to what I am purchasing. So I didn't like that at checkout.

Speed

Fast...checkout was a little slow.

Ease of Use

Maybe the About Us information should be out of the category list and in a different place altogether (like as part of the global header?) It doesn't really fit in with categories. Good use of extra instructions with the category headers (like if there are only subcategories available...that is well explained) NEW category is a good idea too.