A computational chemistry program I know uses at least four external libraries which rely on assembler for their kernels (BLAS, FFT, small matrix multiplication

A computational chemistry program I know uses at least four external libraries which rely on assembler for their kernels (BLAS, FFT, small matrix multiplication, and scalable matrix diagonalization). That provides a factor of several over Fortran, often running on petascale systems. The economics work in such cases, at least; Fortran-callable scientific subroutine libraries are one of the more successful examples of code re-use.