My biggest bottleneck is dealing with third-party code that was written not just without automated tests, but with designs that thwart attempts to test it. I can't prove my code does what it says it does without automated tests, and that's important for the long-term maintenance of my project. Nonvirtual members, whackadoodle inheritance hierarchies with complex constructors in its base classes, depending on resources like the network in constructors, and all-around reliance on static state are all progress-killers.