Holding down Cmd-V at startup will put MacOS X in "verbose" mode, displaying the Unix system message buffer instead of the Aqua splash screen and progress bar. For those who'd rather always boot in verbose mode (and don't want to hold down Cmd-V every time), the darwinfo.org FAQ explains how to set your Open Firmware parameters to support this.
Note that rebooting into MacOS 9 will reset these parameters, so this tip works only for as long as you stay pure. ;-)
Mac OS X Hints
http://hints.macworld.com/article.php?story=20011107045445702