FWIW, I've always heard the joke as "There are two hard problems....", which I find a little funnier because it starts the same as the original quote by Phil Karlton and just adds the joke at the end.

haha, thanks. I haven't heard of any of these. Sounds like a good opening for a presentation.

I know it as

naming things, cache invalidation and concurrency

There's five, you forgot regexes.