>> Is there something more complicated that's actually used?

Yes, absolutely. It's less common but so are the people who can implement them.

This was my indirect way of asking for examples :).

And that was my indirect way of deferring to someone farther down the path than me. But Wikipedia has a detailed overview:

http://en.wikipedia.org/wiki/Control_theory

I was surprised not to see Kalman listed in the people section. His contribution:

http://en.wikipedia.org/wiki/Kalman_filter

Turns out to be important sometimes - like when your sensors don't quite give you what you want. But when things get to that level, I call in a specialist to make sure it's done right - got one on speed dial, he does controls full time all the time.