One problem related to air bag light on has been reported for the 2007 Lexus IS250. The most recently reported issues are listed below.
There has been an ongoing problem with these cars with the air bag wiring harness. Many cars have had this problem including my car. The wiring harness gets disconnected from the air bag itself and disconnects puts on the air bag light. Taking it to the local dealer I was told that it would be $2,500 out of pocket. Looking through the forums many people have had this problem and it is a very normal problem with these cars.