it's real seamless and nice just ends up being expensive after a while if you are trying to do enterprise stuff & their add-on services aren't particularly cheap. The customizability of AWS & private stuff means you have to do a bit of server admin but it is generally cheaper & can give better performance.
EDIT: Oh also note that (my biggest gripe) I see big performance swings / queue-ing issues that aren't really correlated with traffic. Plus they introduce some platform/API changes intermittently that make their admin UIs kinda buggy. Or you have to change your workflow to integrate with their services (though the APIs for this are usually ok). I don't know, I feel like they make a lot of money draining people on threads since the performance of RoR overall is kinda questionable, along with the performance of their platform. I'm going to try with Play framework soon & see if there are less of these issues.
nothing's wrong with it (although it's expensive). I think the point was the Heroku is a service built on top of EC2. Switching from Amazon EC2 to Heroku isn't switching your platform at all... it's just paying for convenience. Personally I think Heroku's convenience is worth the difference. The question is more if the base EC2 pricing (which Heroku adds to) is worth it for your needs.