Anybody knows what percentage of these 60,000 apps are actual paying clients? If e.g. 50,000 of these apps are free, even for a modest cost of $3/month to host each one, that quickly adds up to ~$2mn of cash burn / year.

Another interesting question is how well they scale. http://success.heroku.com/ has some interesting companies, but nothing with very high traffic (or am I wrong)?

PS. I'm a happy heroku user myself.