I've replaced every incadescent w/flourescents except for the outdoor units. Since 1998 (The kid had been out of the house for over 1-1/2 years), my electric bill went from $120.00-$130.00 per month, down to $75.00-$90.00 per month.
And if you look around, you'll sometimes find really good bargains on some decent bulbs. Even better savings.
During the past few years, the prices on flourescents seem to be dropping more and more.