I recall hearing folks at Heroku talk about this before - basically the message was yes, there are many ways to abuse the free service but they rarely have people _actually_ doing it.
Kind of interesting, as it would be pretty trivial to use many single dynos (with shared caching, db) in one account for one application.
I love that they technically let people do this, even though it seems like a "loophole" ripe for abuse. It's a nice attitude.
(For those who don't know – Heroku gives you 750 free dyno-hours per app per month, forever. This is in contrast to AWS, which gives you 750 free instance-hours per month per account and only for the first year, AFAIK.)
It's worth noting that Heroku silently spins down free-level apps that aren't in use (restarting them on a request), so they aren't necessarily consuming all 750hrs of machine time on every free app.
Kind of interesting, as it would be pretty trivial to use many single dynos (with shared caching, db) in one account for one application.