Firstly great site and great idea. But you are not (hopefully) posting here to get your butt kissed but for some constructive criticism and ideas, so here goes:

1. The site is a little busy and lacks a real call to action. "Start Designing" kind of disappears

2. I think you need two sites. One for the business market and one for the consumer market. These could both have the same backend etc, but probably need seperate names / front ends. Businesses (generally) don't buy from consumer related sites and vice versa. Your product definitely seems capable of satisfying both markets (and I would use the current domain for the business market)

3. Your focus both on the site and in your comments here seem to be slightly on the ability to design your own product. Personally I am useless at design so this would not appeal, but I also know a number of people who are amazing at design, but not that good with a blank canvas. I've only taken a quick look at your site but I would perhaps focus on the excellent designs you already have and offering customisations to them over actually having a blank canvas (which is where I ended up when I clicked Start Designing).

But overall looks really good, good luck with it.