It's frequently used here and we have never had any problems. One have to think about a few things tho:
Stuff are being shipped from China so it takes weeks, sometimes months, to arrive.
Clothingsizes are smaller than average. You can find great deals, but you have to up the sizes a couple of steps.
Quality can be a hit or miss. A one dollar shirt can break after one wear or or it can last for years. It's a lottery really. A friend got some really cute dresses for no money at all.
Winter gear is made to suit China Winter (huge country I know so generalising a bit) meaning nothing will stand a place with actual snow or a bit of chill.
I mainly use it for gears (keyholders, watches etc) and nothing has failed me so far
As the things are so cheep and usually shipped in instalments, they're rarely stuck up in customs and you basically don't need to worry about customfees.
In Sweden we can pay by online bills after the things arrive so we never have to pay in advance or if the shipment never arrives which is why it's so popular here.
Edit: Sorry, autocorrect turned some words to swedish gibberish. I've fixed the ones I saw.