I've been a ModCloth customer for many years now and am a really big fan of the website. I find they have excellent customer service, such as when I received a dress with some damage to the fabric and had my purchase instantly refunded. It is easy to get answers from customer service on clothing brands and sizes, and I have not been disappointed in the quality of the clothing.
I tend to only buy from them on sale since full price can sometimes be a bit high, but the sales I have got in the past have been phenomenal. ModCloth is a great way to discover new brands, and I especially like that many of the brands they carry are manufactured in the USA. Returns can sometimes take a little while to be processed, but I am happy enough with the website that it doesn't affect my overall rating.