One problem related to windshield has been reported for the 2004 Lexus IS300. The most recently reported issues are listed below.
Front windshield crack with no rocks hitting it on the bottom mid passenger side. Cracked all the way to the bottom mid driver side about 2ft long. Also started to crack from the mid corner of the passenger side. About 6 inches long. I believe its due to body flex stress that the windshield cracked.