That's a common thought, but as of January they had never defaulted on a loan before (I assume they still haven't, but I read a post from Poloniex saying that back in January). This is because they have an auto liquidate option in place to pay back people who are loaning out coins immediately.
Of course, that doesn't mean that a loan would not be repayed in the future if a black swan type event occurred (such as the flash crash with Ethereum last month on Coinbase). But given Coinbase paid out for that flash crash, maybe Poloniex would as well, so even if it happened it isn't 100% loaners lose money because it is on Poloniex's system if they did not liquidate properly.
I don't have a significant amount of my net worth loaned out, and still believe it is highly +EV to do so, so I'm comfortable with trusting that the past is more likely to predict the future than for something that never happened to occur.
Man, I hope you're right. But the Poloniex TOS say otherwise: https://steemit.com/cryptocurrency/@techwizardry/poloniex-margin-traders-lenders-should-be-very-very-carefull-going-into-august-1st
Yes, there is a slight risk as always. But it requires a lot to go wrong:
I'm closing out all my loans by the 29th. I don't expect there to be any problems, but hey, black swan events happen and as Taleb says, they shape history.
"liquidation attempt to somehow fail (this seems very rare)"
Under normal conditions I would agree with you, but Poloniex recently issued a statement on the hard fork, which said they they may or may not support bcc in the future. Which means that a lot of traders will be withdrawing their bankrolls from Poloniex to get bcc after the fork.
Imho, this is very dangerous for margin traders and lenders as there is less buy orders on the orderbooks of the major alts.