Do You Use Makeup Primers?

Makeup primers are a relatively recent invention, but they've become indispensable for some women. They create an even base for foundation, creating the illusion of smoother skin. Then again, they're one more step in an already lengthy routine. If I know I'll be having my picture taken, I use Smashbox Photo Finish to help my foundation look a little better. On an average day, though? I'm too lazy. Do you use primer?