Over time you will save money.
Being that the bulbs are expensive, it will take a fair amount of time to actually recoup your investment.
How much you can expect to save will depend on how much of your total electric costs are lighting related, and how much the new bulbs actually cost. I have replaced nearly all of my incandescent lamps with compact florescent bulbs. My electric bill declined approximately 5%, enabling me to spend it on computer parts!
Seriously, I believe it to be a worthwhile endeavor!

MAX
By the way, check your local Costco or Sam's for the bulbs. Break even will be that much sooner!!