For me the point where drupal starts to suck is when the core + modules won't do the job. As soon as you start getting into CCK, Views, etc. you're skating on the edge of real development, without any of the tools that make that productive. Writing PHP code in a textarea is not my idea of a good time. And if you have more than one "developer" working on it, fugehtaboutit. With so much stored in the database, synchronizing changes among various developers is nigh on impossible.