A study done by PG & E showed that:
“When PG&E began its 2006-2008 program, it figured the useful life of each bulb would be 9.4 years. Now, with experience, it has cut the estimate to 6.3 years, which limits the energy savings. Field tests show higher burnout rates in certain locations, such as bathrooms and in recessed lighting. Turning them on and off a lot also appears to impair longevity.”
This would make a meaningful difference in cost savings calculations.