Two 40 W incandescent bulbs in the front bathroom burned out within a few days of each other. Being that type of guy, I know that I installed this bulb nine years ago:
The date is easier to read with the bulb in hand: 13 Feb 05. The (5 yrs) indicates the previous bulb in that socket lasted five years.
The other bulb date went in during March 09, so it survived only five years; the previous bulb lasted 6 years.
Even though 40 W incandescent bulbs are history, maybe I have enough spares on the shelf that the next owner can replace ’em with cheap LEDs.
This may not be science, but it does have numbers…
The Smell of Molten Projects in the Morning 
I started coding our CFLs when we got short life out of them. Now, we shifted to LEDs in the hard-to-access fixtures, so we have a lifetime supply of CFLs. The incandescents are reserved for when we need the heat, or appliance duty. (Two bulbs will keep an insulated pumphouse from freezing most of the winter. We have a third one on a thermoswitch when it gets really cold, like the -28F morning we got last winter.)