One problem related to side/window air bag has been reported for the 2008 Cadillac STS. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2008 Cadillac STS based on all problems reported for the 2008 STS.
The information window under my speedometer warned me to check the driver side air bag. It then went off about 2 days later. I warned me again in the middle of April, beginning of may and may 22nd. I did not drive my car today (5/23) so I don't know if the warning is still on. If it is I will write again.