so the headline on CNN.com's article about the Mumbai train bombings speaks of "timers hidden in pencils."

No, you idiots. "Pencil timers" are thin-walled metal tubes containing two kinds of acids which will cause an exothermic reaction when combined. Usually, these acids are contained in thin glass ampules separated by a bit of copper (the copper's thickness can be varied to vary the time it takes for the acids to eat through it and combine). To activate the timer, you pinch the tube to break the glass, setting the acids free. Then you walk away unobtrusively to avoid getting caught.

However, given the precision with which the bombs were coordinated, I seriously doubt that the bombs were activated using pencil timers, and that the presence of said timers is a bit of a red herring.