I used Heroku for hosting my php site (http://sea-hag.net) for a while on the free tier. It was OK, but the DB add-ons were all pretty terrible (even on the lower pay tiers). In the end, I ended up getting a VPS and hosting it on that. Now it's lightning fast and I can't complain.

Heroku held its own for a while. I'd recommend it if you need to do some quick testing and get people on it to start, but I wouldn't pay for it.