Well done! Some feedback: Resize your product images ("/images/I/8137AFcYkrL._AA1500_.jpg") or request smaller ones. Remove whitespace before DOCTYPE. Try to avoid session/state URL's: dzYzMzJfNTAzNg==. Specify Canonical or apply www to non-www redirect. The homepage contains content, but this is only accessible with javascript and styling, or without javascript and styling. Consider a <noscript> warning or giving a user and searchbot access to the content with styles on, but javascript off. Adding to this a matter of taste: The background is like the background for iOS touch browsers when the end of a website is reached. That texture has some meaning attached to it for some, that make it in my opinion rather unsafe, to use for other design elements on the web. There is (possibly due to heavy load) a good 6-7 seconds between the dissapearance of the loading graphic, and the loading of new content "tiles", maybe you can add an onload callback for removal of loading graphic.

And a question: What is your organic SEO strategy? Will all visitors come from social? The website behaves like a web-app, so there is very little content to rank with. Are these personal shopping lists publicly available? What happens if people share these shopping lists? I don't see them indexed (yet), so they might not be flowing any link juice. Could you add a blog or something?