I published a paper this year that used it directly and even proposed a modification of it to model job time for a distributed execution environment with a centralized master governing scheduling, task serialization, etc.

When you talk scale-out of any large system, or manycore whatever, Amdahl's law is absolutely fundamental, and when you hear someone say "perfect horizontal scalability," Amdahl's law governs when that will no longer be true.

People who do theory on distributed algorithms use it even if they don't realize it.