I would like to learn more about Amdahl's Law and other similar topics. In what branch of computer science would one place Amdahl's law? Could someone point me to a textbook or further reading (aside from Wikipedia or other sites that are found on the first page of a Google search) that discusses it?
Amdahl's Law is perhaps most associated with computer architecture (Gene Amdahl was a computer architect). Although initially applied to the potential speedup from partial parallelization of a task, the formula applies to the benefit from any partial improvement.
In its general form, it can be applied to many different types of problems. E.g., the improvement in voter turn out by getting a fraction of potential voters to always vote.
Since it is a rule of thumb intended to compensate for excessive expectations from dramatic improvements in part of a system, it is most useful when the improvement factor is large and is intended more for quick estimation (and generally the best case--though sometimes an improvement can unexpectedly benefit other aspects) than an exact measurement (as systems tend to have complex and subtle interactions). (Quick estimation facilitates quick pruning of paths of exploration.)
As a mathematically based rule of thumb, it is not an especially deep topic (rules of thumb based on history, economics, etc. are generally more susceptible to discussion), though Gustafson's Law points out that context is important. However, Amdahl's Law is an important corrective to optimism with respect to dramatic (but partial) improvements.