Nah, I've actually written quite a bit about Heroku (I authored a book on it). The issue was us having complex problems with Django and our supporting libraries: we needed to have database connection pooling, we had to rip out the tastypie REST framework due to complications with scaling the user model, and a bunch of other stuff.

Heroku has always been great for us!

I'm always a bit surprised about the RapGenius stuff because their problem is not really a Heroku specific issue, IMO. If you're running code on Heroku (which uses random load balancing), you need to have a proper multi-threaded web server to serve requests concurrently.

In our situation, we were able to service many concurrent requests per dyno, and maintained very low response times (10ms or less), in most cases.