Kernel-2.2.5-15 (the default included with RH6) panics on bootup as it tries to probe my SCSI controller (an Adaptect AHA 2940U2W) for devices. If I disconnect all devices from the SCSI board, the kernel boots successfully. Turns out that RedHat's kernel packages include v5.1.15 of the aic7xxx patch. Installing the kernel SRPM, replacing this version with v5.1.16 of the same patch, and rebuilding the kernel fixed the problem. It'd be *awful* nice if you could incorporate this newer patch version into the standard kernel.
Should be there in 2.2.5-22 available on the updates site.