Do you want to enable Expires: headers on your Debian web-server? It takes three steps:
Update: I hadn't realized how many non-static images I had on my server. Pretty much any script that generates graphs from realtime data, for instance. I have a lot of rrdgraphs and the expires header breaks them. Oops!
All this is motivated by Yahoo's guide for speeding up websites. Along with the YSlow tool webmasters have no excuse for not knowing why their site renders slowly. Some of their suggestions are a bit complicated for a small site (no content distribution network for my blog, sorry). But any serious web company should take a long hard look at its reports.