Selling PowerBook -- securely erasing hard drive?

I would think the most industrial-grade erase utility would probably suffice. (Which are you talking about? Permanent Eraser, perhaps?) You could boot the PowerBook into FireWire disk mode (press the "T" key upon rebooting it), and then from another machine, access it as an external Firewire drive and use the disk utility to obliterate the contents.

That should be sufficient. But if you still wouldn't sleep well at night even with that, you could always swap in a new hard drive, even though it's an added expense. Depends on your ability to trust the utility and feel at ease.

What I'm wondering is if the 35x erase on Disk Utility that comes with Mac OS X 10.4 is sufficient? Do we really need a third party disk utility like Permanent Eraser?

Probably and probably not, respectively. I just thought it sounded to me as if you had a third party utility. Actually, I think the Disk Utility in OS 10.3.x and 10.4.x has the same 35x erasure, so you really don't need it under Tiger or Panther. Though I should point out that Permanent Eraser is freeware.

Actually, I think the Disk Utility in OS 10.3.x and 10.4.x has the same 35x erasure,

Panther (at least up to 10.3.4) has "8 Way Random Write Format." I do not know about Tiger's capabilities in this area (though "35x erasure" sounds quite impressive).

If I were selling my PB which had contained sensitive info, I would feel comfortable selling it to an anonymous user after having performed the 8 Way Random Write and installing a new OS.

Of course, if I were selling it to a government spy who was personally out to get me, that would be a different story, and as has already been suggested, I'd simply spend $70 or so and install a new HD. $70 for peace of mind regarding information that must be terribly sensitive is pretty cheap. If it really is that sensitive, why take any chance?