My Windows' Explorer crashes with some regularity. (Get all of your childish Mac and Linux comments out of the way now - I'm unlikely to ditch Windows anytime soon.) When it comes back to life, which it does automatically, some programs in the notification tray (that thing with all the icons near the clock) don't come back with it.
It's not that those applications aren't still running, but that they were - for some reason - never told to restore their icons into the task bar.
