Dave,
Those in Cali are stuck using 92. Your car should be fine :
The manual then states you won't necessarily harm the motor with only 91 octane. It simply will play with the ignition, an potentially reduce power, so as to limit any detonation.
In many places 91 is the highest and many people are using it without issues. You may see a reduction in performance with 91, but it would be hard to test and statistically prove a performance difference with 93 over 91 for the consumer.
http://986forum.com/forums/showthread.php?t=11897
Nick