Two days ago "CoinWallet.eu" announced that they were going to do an "Ultimate" Bitcoin stress test, flooding the network with transactions. It looks like they are in fact going ahead with that.
Specifically they claimed they would spend 20BTC - about $5kUSD - to create transactions with a fee of 0.1mBTC/KB. That works out to 200MB worth of transactions, which will take some time to be mined.
Transaction fees are a supply and demand marketplace. On one side you have the supply - up to 1MB worth of transactions approximately every 10 minutes - and on the other side you have demand - what fee/KB people are willing to bid to get their transactions mined. With few exceptions essentially all miners use the profit-maximizing algorithm in Bitcoin Core to choose transactions: start with the highest fee/KB transactions, working down to the lowest, stopping when you're