A few days ago I pushed an update to the site. Although everything tested fine locally, apparently one of the included changes introduced a serious bug impacting performance. I haven't tracked down the cause yet, but I've rolled back the code which seems to have helped:
Sorry about that. :(
It may take some time to track down, and the odds are high that I'll push a bad release or two out while trying to bisect down to the exact bug - and it takes a few minutes of monitoring to even notice that it's occurring. So please be patient.