In late 2015, I suffered the loss of 500 DASH coins when the Cryptsy exchange went offline. I had been converting Bitcoin to DASH, and decided to leave the coins on the exchange hoping to make a switch back to Bitcoin in short order. With that lesson learned, and knowing what went on with the MT. GOX debacle, I no longer leave my currency on an exchange.
Today I tried to log into my Coinbase account with the intention of buying a few more Ethereum, but they are having issues with the website. We will see if they get it up and running again, and I will patiently wait knowing that my online wallets are currently empty.
My sympathy to those that are currently unable to get to their funds. I hope when and if they do get it back up, they do not suffer from a "bank run", only to have to shut the servers down again. I like how easy it is to purchase BTC with fiat on their website, but I will never leave anything in my online wallets ever again.