I like it, in a qualified fashion. For apps at the scale I operate at, which don't really benefit from the scale-to-the-moon aspect, the main selling point is the ease of deployment. You have to balance this with there being many, many headaches if you decide to use gems/libraries which interact poorly with Heroku's view of the world. I had to do an awful lot of R&D to get a client's project working, and that was for a wee little website which mostly turned strings into other strings.

Personally, at my combination of developer and sysadmin ability, I find using VPSes is a better use of my time. For client work where I want to hand over a product which doesn't require my ongoing involvement? Heroku all the way.