HHVM is the answer to the following conversation:
P1 - "PHP sucks, it's a terrible language with no proper design and no serious person would ever want to use it"
P2 - "But tons of large projects are built on it and people ship with it everyday"
P1 - "So? It's still terrible"
P2 - "What do you think is so terrible?"
P1 - "Oh lots and lots of things, I wouldn't even know where to begin"
P2 - "How about this: let's throw boatloads of cash on it for a while and see where we get."
P1 - "Oh gee, I dunno if..."
P2 - "Boatloads of cash it is.
[edit] After seeing how my comment could be seen as ridiculing HHVM: I'm a PHP dev and I'm loving every second of what they're doing. I think they're right on the money.