We mentioned it before (a and b), but we will say it again. Some Mac models have had another startup problem (beyond the blinking question mark problem that has been getting most of the attention): namely an approximate 30 second delay between when you turn the Mac on and the startup sequence begins (typically, the screen remains black during this time). This was first noted in Mac OS 7.6.1 and continues in Mac OS 8. Neither Drive Setup 1.3.1 nor the Firmware Utility 1.1 seem to have any effect on this glitch.
Darren Burgos has this problem on his Power Mac 6400. He has started a new thread in Apple's Discussion Boards on this matter.
[P.S. This problem seems to be something more than a delay due to a RAM check or due to no startup device selected. A PRAM zap may help but is not a permanent cure.]
Update: Apple has informed me that "we know what the issue is and we feel we have a fix, we just aren't sure whether it will make it into the next update."