Winamp.
I noticed the other day that the 'enqueuing' functionality had disappeared from Winamp, which was mildly irritating, as it's really quite useful. I searched the changelogs.. no mention, then I remembered it was part of a plugin, JTFE.
Quick download, install using the installer, reload Winamp and.. nothing. No enqueuing. No extended jump-to-file dialog. And, furthermore.. no mention of the plugin in the list of "installed plugins" (which really seems just to mean "plugins in the .\plugins folder").
I tried poking it a bit, system log, dependency walker to check it wasn't looking for anything and dying silently, etc.. no idea. Last ditch attempt, re-install Winamp, no luck.
This necessitated me re-installing the last.fm plugin, which, although it loaded, and was submitting plays, bombed out Winamp trying to enter the configuration dialog. Quick search of their (actually useful) forums quickly came up with this post, which suggested turning DEP off.
This fixed the last.fm plugin, but also, surprisingly, fixed the fact that JTFE wasn't loading. Assumably something's trapping the DEP error it's encountering on load.. didn't know applications could do that, doesn't sound terribly good for security...