I’ve been using CFL bulbs for the last 5 years or so in select lamps and have been slowly switching over to CFL bulbs for all lights around the house as my old bulbs break. But I never knew that they contain mercury which means this:
Like batteries, used CFLs need to be disposed at a toxic waste depot rather than tossed out with the ordinary household trash. Because mercury is cumulative, this poisonous element would add up if all the spent bulbs went into a landfill. Instead, the mercury in dead bulbs is reclaimed at such depots and recycled.
The most important thing to remember is to never use a vacuum. A standard vacuum will spread mercury containing dust throughout the area as well as contaminating the vacuum.
Apparently, there’s enough mercury in them to not be good if you breath much of it in or get cut by a piece of glass from the bulb. I can’t remember for sure if I’ve ever broken a bulb, or how it was cleaned up if I did.
More information here: http://www.snopes.com/medical/toxins/cfl.asp