I've never bought clothes (dresses, blouses, jeans, shoes) online, and I doubt I ever will. I'm very particular about the way things fit, and I would hate to go through the hassle of returning things when/if the y don't fit.
I have, however, bought t-shirts and hooded sweatshirts online, and have never had a problem. Those don't typically have a wide range of different "fits" though lol.