I've been writing Rails for near on five years, and there are some things that really grind my goat. Rails is great, but there are so many things we get wrong, both as a framework and a community. In particular, for applications that have grown beyond an initial prototype (if you earn a salary writing Rails, this is probably you), many Rails Best Practices are actively harmful to creating solid, robust, and enjoyable applications. I'll talk about testing, data modelling, code organisation, build systems, and more, drawing from a large pool of things I have seen done wrong and also personally failed at over the last half decade. Of course I'll be providing suggestions for fixing things, also.
It's more of a freight train, see.