Yes, a few times. As a traveling trainer, I made over 400 flights in 7 years, almost always in standard, where my shoulders would be squeezed by the people beside me. I got boosted to first class a few times, and it was fun, mostly simply for the larger, more relaxing seat. (More airplane food is still airplane food, and I don't drink.)
For long trips - transcontinental or overseas - it is a really nice feeling to have the extra space.
And one perk I liked - being able to get a soda or seltzer even before the plane took off.