Lost and found (files)
Euan Williams some users may be mystified that when a file, perhaps on the desktop, is "placed" inside a folder it can disappear if there is a mouse glitch. Find-File and Spotlight see it, but the user doesn't.
A corner of the little offender's icon may be found lurking in the corner of the Finder screen (top left, with Lion). Catch it by the tail and put it back in its cage. Voilà.