I was never a fan of automated workers in Civ4 or BTS, particularly without "leave forests" or "leave old improvements" turned on. Lately, however, I've found that managing my workers in FFH starts to get tiresome. Lots of workers, lots of area to cover, replacing early improvements (forester's lodge, mine) with lumbermills or windmills later on, etc.

How does the worker AI do in Orbis, especially without the options to leave forests or improvements turned on? Does anybody use it?

Yep, and they leave forests and old improvements too. They do occasionally build unnecessary forts though.

Although fort commanders are pretty nasty. Particularly for Mechanos.