If you go to https://bitcoinfees.21.co/ now, you will see that there are many cheapskates or maybe spam transactions under 1–30 satoshis per byte transaction fee. It roughly means there are many transactions trying to pay with under 3.4 US cents (BTC price: $437, median transaction size of 258 bytes). Forty percent of it are paying with 1.1 US cents.
The number of unconfirmed transactions you see here is just an illusion. The average fees charged under Bitcoin exchanges is roughly 100 bits or 0.0001BTC (4.4 US cents).
I think exchanges should adjust their fees accordingly with such attacks. Using a fee of 160 bits (0.00016BTC, 7 US cents), you wouldn’t feel any delays at all.