I used to. My primary trading was done at 10x futures. However, with all the rumors surrounding Okcoin (bad security protocols, front running their customers, making the market with un-backed accounts) I moved my funds elsewhere.
I have asked them to do a proof of reserves and publish balances managed by them - really hoping they are doing it.
the thing is, how much trust can you put into that? there was a reddit thread recently where the former CTO stated that Okcoin gamed the audit. here's the link:
https://www.reddit.com/r/Bitcoin/comments/37tm1b/czs_statement_regarding_the_dispute_between/I can confirm OKCoin removed a number of accounts (used by OKCoin bots) to pass the Proof-of-Reserve audit in Aug 2014. In essence, these bots trade on fractional (or fictional) reserves. Stephan Thomas was lied to during the audit. This is an unfortunate limitation of the proof-of-reserves method.