Well that was an incredibly satisfying exercise. I attacked Facebook. For some reason I am friends with a number of fictional characters. They all went. And anyone whose name was unfamiliar.
I also had time to have a go at my lists. This is an incredibly useful Facebook feature which allows you to share items only with certain people -- I use it to avoid horrifying non-parents with questions about newborn poo colour; and so that I can share local lost dog / teenager posts only with people near home. Here are the instructions in Facebook help for adding and removing people from lists.
Another useful lists feature is the Acquaintances list -- this allows you to see less of certain people's posts in your timeline. So if you've got a friend who is always going on about... eg (trying to think of a fictional example so as not to offend anyone) er... Fireman Sam, you can silence them. Here is some more information.