Well after wiping the book this morning and getting everything reinstalled (huge time-saver tip: keep all your 3rd party apps in an Applications folder in your Home folder, this way OS X can still find them, yet it's easy for you to back them all up), I found I was still having these kernel_task issues - even before I installed all my extras. Getting frustrated, I finally decided to do some googling and discovered that, once again, MacOSXHints had already gotten to the bottom of this issue.
As it turns out, this kernel_task usage problem is a result of Apple's own trackpad software horribly misbehaving on these latest PowerBooks, even on a 100% clean system, which I verified this morning. MacOSXHints did find a 3rd party solution in the form of SideTrack, a shareware trackpad software replacement for PowerBooks and iBooks that has a few neat tricks up its sleeve. While I can verify SideTrack fixed the issue on my PowerBook, it alters the behavior of two-finger scrolling and, of course, costs money ($15). I also can't stand some weird thing it does to mouse movement and acceleration; it feels and acts differently than Apple software, and these two dings caused me to uninstall it and take my chances with keeping kernel_task happy again.
Moral of the story: Apple needs to fix their PowerBook trackpad software, and soon. This kernel issue destroys productivity, usability and battery life, and also causes a PowerBook to get pretty hot. If you're running into issues like this (or any other kind), I urge you to add your voice to the pile at apple.com/feedback.