The site code now uses Markdown, both for the blog posts and, most importantly for you, in comments. Go on, try it. Everything except trying to insert XHTML ought to work.

Does this situation feel familiar to you? You're writing some kind of system that has to support several clients, or players, or just plain actors, at the same time. A networked multiplayer game would be a good example. Now, the practicalities mean that incoming data (from a network socket, for instance) needs to be handled concurrently; in other words, you can't decide to block for one client while performing some action and ignore everyone else. But you still need to preserve state.