How often does the fuel filter need to be replaced, and where exactly is it located?
What are the symptoms of a bad fuel filter or fuel pump?

I'd say change the fuel filter(s) every 30,000 miles or 2 years. My '93 740iL has two fuel filters located up inside the right rear wheel well.

Symptoms: obviously if the fuel pump fails altogether the engine won't run at all. If the pump is sparatic or the filters are very dirty the engine would run rough.