I'm using poloniex for trade as well as form lend a small amount. And i never had any problem with lending and as above mentioned, poloniex taking collateral from their users so even if the your loan taker has scammed you can still get your money back.
Is this safe? Ask Karpeles.. 
Polo s quite safe, they make a lot of money from their operations and the only real danger would be some form of hacking.
Where can we find the financial report of Poloniex? I trade some coins there, but not sure if it is really safe.
Just take a look at daily volumes and multiply that with their fees. Not to mention they take 15% fee from margin lending.
But I wonder how much bitcoin poloniex have in their bitcoin addresses though. I'm just worried that they have enough money to say "We have 20 million dollars worth of bitcoin? K. We'll shut down the site and claim it was hacked. Ez $20 mil."
I doubt they only have 20 milion inside them,sure when the pump starts and i remember something around 50k bitcoins around just eth besides the others altcoins,big holders,whales sure they moove their coins in and out avoiding taking huge risk and if something happens to poloniex they had taked out their main porfolio,playing with profit just.