One example is the module elasticity-updated in DOLFIN for which
assembly time dominates solution time (using the old form evaluation
system in DOLFIN). This would be a typical example of a system which
is more complicated than Poisson and where assembly time may be
significant.
This is a good point. There are these complex-model linear problems
where you just form the matrix and solve. Is that what you were
thinking? Since you can vary the elasticity tensor these days with
special materials, one could even imagine optimizing over varying
elasticity tensors, in an extreme case.
Ridg