We had a major spot of downtime yesterday, from approximately 17:00 - 20:00 EST. The issue was caused by a series of bugs that compounded upon themselves, eventually grinding our serves to a halt. We've fixed these issues and things seem to be running smoothly, if a little slow today. The issue right now is certain parts of our caching code -- which is one of the key ingredients for speed -- seems not to be always triggering, causing a certain query to be executed over and over again when it doesn't need to be. We'll try to fix this today in development and put the fix into production early AM tomorrow.
Sorry for all the problems.