Right, but Facebook supposedly receives 1 billion new comments + a couple billion likes + a couple hundred million status updates daily, and is probably the largest photo sharing site on the net. Twitter gets about 200 million tweets daily and Reddit has 250 million comments total. Disqus is not much larger than Reddit.

So, since most people here are suggesting Python or Ruby, what real world example can we provide that compares to Facebook in order to make sure that these languages would perform better than PHP?

Neither Twitter, nor Reddit or Disqus are exactly the most stable and performant sites out there. So?

I would say that quick and dirty comparisons like this are meaningless.