According to some early testers of the 3850 and 3870, users encounter random freezes of the screen or no boot. This seems only to happen on the Intel P35 chipset and not on the X38 chipset.
Another observation is that such problem only arise when the FSB is raised beyond 1066. The early tester tested one on MSI P35 board and tells us that the issue is very apparent. Sometimes, the driver can't be recognised and the system will not allow you to reinstall the catalyst driver.
Radeon HD 3850 and HD 3870 will launch next week. If you intend to purchase one and pair it up with a P35 chipset mainboard, i hope you won't be pulling off your hair with weird issues during the overclocking of your CPU. It will probably require a firmware fix or driver update to solve these strange issues during overclocking.