It hasn't happened to me yet, but judging from the forums and some peoples' names, it seems like slow-play griefing is a pretty serious issue. I've thought of a genius fix for that, if the staff are willing to tinker with the business model a bit.
Instead of (or, if you must, in addition to) charging for expansion sets, have a subscription provide a certain amount of rated-game think time per month. Maybe you get 30 minutes or so for free, and if you play the game alot, you get a sub for another 60. But griefers who make one game take 30 minutes are shut down completely unless they want to pay through the nose. Meanwhile, if you aren't playing Very Seriously, and want to just mess around with friends or teach newbies, you can take as long as you want in practice mode.
This solution requires no reporting, no investigation, no banning, just a tweak to what you get for your money, and the problem is instantly gone.