My Powerbook G3/333 is running like a champ on OS X, with a 128 MB chip up top, not Apple installed.

So some, but not all are having the issue. perhaps we could pull and compare RAM info? Perhaps it is a similar issue to the G4 Firmware upgrade, something required for stable operation of the Mach kernel? I'm no tech wiz, just tossing ideas out. =)

Not all, but quite a few.

The best theory out there right now is that there is a batch of Lombards out there with faulty CPU cards, and that OS X has brought out the worst side of this hardware issue. I had an affected Lombard, replaced my CPU card with one from pbparts.com and now I'm running totally freeze free with the same RAM that behaved so horribly before.

Besides replacing the CPU card, the only reasonable idea for a fix that's been circulating is a firmware upgrade from Apple. Depends on just how serious the problem on the bad CPU cards is I guess - it was minor enough that OS 9 only froze from it every other day or so on my system (compared with 30 minutes or less in OS X).