I haven't. They have a lot of pretty dresses though.
But there's lots of problems with buying prom dresses online, not just from that one site. You may like the way it looks online but when you get it and put it on you may hate it. That's not the website's fault. It's the same thing as when you see a dress on a hanger/mannequin and it looks great, but looks awful when you try it on. It's because you probably don't have the same body shape as the model in the picture/mannequin. Personally, I wouldn't buy a prom dress online. I'd want to try it on before I spent so much money on something. Of course, you could end up loving it and it may only need to be hemmed or something minor.
You could always look it up and see if a store near you is selling those brand of dresses.