It's the driver head on 03's only. I've personally never heard it, however, and i've worked on and driven over 15 03's with all sorts of mods.
It has never been proven to cause engine failure but most people change to the redesigned heads out of caution.
"I'm not driving too fast...just flying too low"
-03 SB Cobra vert- 2552 of 5082 Born 02/25/03
90 7up vert - new project-07 DSG Focus -DD