Let me preface the following with the qualification that I don’t like federal mandates for these things. However, I adopted these things (CFL’s) back when they were $5 a pop, without the subsidy. The reason? The payback threshold for these bulbs is pretty low. A 100W traditional bulb-equivalent CFL uses 26W of energy. That’s 74W of savings. If they last 1 year, a mere 2 hours a day of usage results in the full recovery of the bulb’s cost, assuming power costs $0.10 per kWH (74 x 2 x 365 / 1000W x .10) = $5.475.
If you were in California, the higher tier rates for most are more than $0.30 per kwhhr.