I just had my plugs changed today. I had Autolite 104'* with a gap of .050". They were in the motor for 2 years. Now, I know it is recommended that these things get changed once a year because they are 2 ranges colder than stock, and they are copper.
Here is a pic of what one of the plugs looks like:
They didn't look too bad to be honest. The motor still ran good, and I never had misfires. I will get these changed again in one year just to be safe, but I'm suprised these lasted a long time, considering people say to change them more often.