Ask HN: How many instances are you running your app on?

Would love to find out how many instances people run on versus the traffic they get. The only articles that mention this info are the run-away hits with millions of hits a day, on highscalability blog etc.

I wonder what the upcoming startups are running with a rough range for traffic [if you're willing to share that.] Also would be interesting to find out your monthly expenditure on infrastructure.