With the new computer controlled engines, it would appear that octane rating is not as critical to prevent pre-ignition as in older engines. These engines will self adjust and run on 87 octane. However, as stated by others in this thread, you will lose some performance and in my experience some gas mileage (1-2mpg).
Now the economics. 92 octane is generally $.20-.25 more than 87 octane. My logic says that in a typical 20 gal. fill up, I'll pay roughly $4.00-$6.00 more per tank. In my opinion, that aint bad for a tank of higher performance, and better gas mileage. Just a thought.