I just changed 26, 60 watt conventional bulbs with the 60watt equivalent 13w "green" long-life bulbs. Let's do the math:
26 x 60 = 1560 watts
26 x 13 = 338 watts
That represents a 75% savings on wattage--pretty impressive. Ok, a six-pack of these things at Walmart is $10.98, so that's $1.83 a bulb--not sure how that compares to an incandescent, but it seems very reasonable to me. Also figure in less heat generated, less pull on your overall house power, and 5 year bulb life (average for argument sake).
I've got more replacing to do. I need 2 more 60watt equiv, and 13 40watt equiv bulbs (damn ceiling fans) to finish the house. My kitchen main fixture uses 5 flood style lights, for which I haven't seen a new "green" bulb replacement for yet. Cripes, have you ever counted how many light bulbs you have? You'd be surprised. We have a 3 bedroom/1 office 1950 square foot home--it's not a mansion by a long shot.
In case you are wondering, looking at an incandescent 60 watt bulb, right next to the new 13watt (60w equiv) green bulb--the new bulb is actually slighty brighter, so the "equivalencies" are accurate FWIW. Seems like a winner all the way around.