That's a great example for comparison. Sometimes reddit goes down completely, maybe more often than most web apps. But it's still uncommon enough that I think of reddit as a site that "works" and I go into a session expecting it to go smoothly.
I don't think I've ever seen OkCupid down completely, not that I use it nearly as often as reddit. But I've never seen reddit have the behavior that while it's up, I can expect one of every 5-20 page views or posts to time out or fail on the first load/submit but succeed on the second or third. And this is consistent enough with OKCupid that I think about a usage session as something I'll have to be in the mood to fight with.
