while remaining dead simple to use, heroku is also becoming an increasingly sophisticated platform, capable of handling a wide variety of app requirements. eg - background workers and memcached support are available in beta. since i started using heroku for tripeedo.com, the traditional server hosts are looking a lot like dinosaurs.
It's worth pointing out that Google App Engine + JRuby & Rack Apps is considerably cheaper than Heroku.
You can build a full Rack app w/ DataMapper, one that is portable (i.e. no lock in) and scalable, w/o having to pay anything, prior to some serious traffic.
(Caveat: Tool chain for Ruby on Google App Engine is a little raw at the moment, but it's coming along)
That's not the point. The point is to deploy in 15 minutes and then -never think about infrastructure again-. In the early days, anything that's keeping your product from customers is getting in your way.
Yeah, and with AppEngine, you can build an app, deploy it, and continue to hack on it, and improve it without having to pay any money, Heroku gives you 5 megs of space free, yeah? AppEngine's currently limit is a gig of storage space, 46.3 CPU hrs, 10gigabytes of incoming, and 10gigabytes of outgoing traffic PER DAY.
Both EC2 and Heroku cost you money as soon as you start to use them.
So, sure i will agree, it's easier to get up and running on Heroku if you're a vanilla Ruby dev. AppEngine's scaling is a lot more sensible economically imo.
And this absolutely not to knock Heroku, they are doing some really cool stuff. But for speculative projects, AppEngine is nice, and free for a lot of uses.
To be fair, Google AppEngine gives you that same ability. The difference is, you have to build your app for AppEngine rather than building a plane jane vanilla rack/rails/sinatra/whatever app with postgres.
The app I have running on Heroku uses a number of prebuilt gems, including things like twitter-auth that sort of assume you're using migrations and ActiveRecord with it. I may move it over to AppEngine at some point, but the absolute fastest way for me to get an app up and running was with Heroku.
The goal that i have as someone who's building tools for GAE, is to sufficiently abstract the GAE tools so that you aren't building specifically to AppEngine's infrastructure. DataMapper is a great example of an abstraction layer that allows you to build application code that is portable across infrastructure.
The goal is to be able to build an application on GAE, and if your requirements change at some point and GAE doesn't fit, you can migrate off of it without substantial pain.
Additionally, it's pretty quick to get an application up and running on GAE as well. Not entirely trivial at the moment, but it's getting close (still waiting on the release of a couple gems before i can say that's the case).
I'm really happy with the easy to deploy options being made available. I'm not too sure about the "it scales" attitude with any of these products. Scaling is not about the platform, the platform is one component.
Once you get used to it, it really is amazing to deploy apps in 2 minutes and not do any sysadmin, and know that it can scale.