I just posted some details on extending the life of enlarger lamps. The 30,000 foot overview is that reducing the voltage can substantially increase the life of a bulb. This follows the formula of (Design Voltage / Actual Volatge)^12, so running a bulb at 110V instead of 120V can extend it's life by almost 3 times. This came from the May/June 2000 issue of Photo Techniques, which has an article “Optimize Enlarger Light Intensity” by Conrad R. Hoffmann. It focuses on reducing the light output by dimming, but touches on the lamp life benefits as well. Worth a read if you can find a copy.

I figure this will be of use as more and more enlarger bulbs go out of production.

Also, this is not a good idea if your enlarger has any type of electronics in it. I am only recommending this for simple condenser systems that have a bulb that plugs directly into the power outlet on your timer.