It sure CHANGED my electric bill.
My home had cathedral ceilings where the designer of the home got "can light crazy". I had 20 in the great room area and over 20 in the master bedroom/powder great room, and in the family room not to mention the multiple lighted sconces over each bathroom and kitchen. :R
I changed all my lights to CFL actually just to see IF it would make a difference, and it DOES! Cleared off over 1/3 of my electric bill in one fall swoop.
Don't like that they are Mercury, yes you drop them and they are 100% going to shatter all over.
I have yet to see a recycle for them so off they go into the garbage. The mercury and the vast amount that will hit the landfills is sad, but saving $100 bucks a month on the electric bill is enough for me to use them until the power company stops raping us.