One of the more annoying bugs in Windows XP is the tendency for the Task Manager icon to not show up in the tray (aka the notification area). Sometimes it does, sometimes it doesn't, and it's not consistent enough to have an obvious cause. Looking on Google turns up a bunch of forums that have the same problem but no working solution.

Why does the task manager icon sometimes not show up? How can I repair it when this happens (how can make it show up when it's missing)? How can I prevent it from not working in the first place, so that I don't have to worry about repairing it after the fact?