On the overall, I like Modcloth. I have ordered from this store several times over the past five or six years. I like their selection and I really like that they cater to the plus size market too. Out of the 20+ pieces I have ordered, about 2/3rds have been well-made.
Since they have different designers, some things are wonderfully made; others, not so much. I ordered a cotton dress where the material was so nice and sturdy that people commented that it looked like it had been made decades ago before all of the fabric downgrades. I ordered another dress that was supposed to be okay in the washer, but shrank so much that it was unwearable as anything other than a top.
The only real complaint I have with Modcloth is their direly slow shipping. I ordered clothing for a vacation once, four or five items, about a week before I was due to leave. Despite paying through the nose for two day shipping for it, they didn't arrive on time. I contacted customer service and they were nice, and they completely refunded my shipping and gave me a 25% off promo code, but told me at that point I had to contact fedex. Fedex was not so nice and they did not arrive before I left for vacation.
Generally speaking, their "savvy saver" shipping (the cheapest) usually pushes the limits of their 9 days max promise. The galling thing about that is that I only live a two hour drive from their warehouse's location, but they use a convoluted service that starts out with Fedex and ends with USPS. I think if they used another service and even if it raised the cost of standard shipping, it would still be a lot better for their customers.