Just read the notice on Poloniex. I must say it's much better than Bittrex, they won't even block users from withdrawing their funds, while Bittrex won't even update the fact that you're not allowed to withdraw, or even the reasons why you can't withdraw, and from what I've been reading and experiencing, they won't even email you back when you email them about not being able to withdraw (keep in mind that at first you have no idea what's going on). It sucks that I will have to send them my ID in order to get all my money out and use another exchange. And I rather not use Bittrex again simply because the way in which they are handling this just feels very, very shady, that it really does not make me trust what they would do with users information. Look at how Poloniex actually gives you a warning, versus complete secrecy by Bittrex.
They have and they are blocking withdrawals. In fact the very same people that made polo what it is today are the ones getting screwed by it right now as we speak. waiting months to remove what you have invested for years is a tough pill to swallow especially while you are watching your return evaporating.
Anyone using polo for anything but penny trading of shitcoins is screwing themselfs over and has no one to blame but themselfs when they get boned. the warnings are all over this board and the interwebs at large.