I guess I was lumping everything that used the MPC106 (aka "Grackle") in one of its various forms together. In any case, maybe it's bad karma but I've had *terrible* luck with DIMM compatibility with all of those machines. SDRAM DIMMs that worked flawlessly *for years* in some rotgut Pentium II/III (usually with a 440BX-based motherboard) running 24/7 as a server almost inevitably gave my B&W heartburn, and I had similar luck with SO-DIMMs in the iMac. (These were DIMMs with the correct configuration that were detected as full size, they simply didn't work properly and caused kernel panics, hard disk corruption, etc. Oddly DIMMs from similar vintage Dell machines almost always work, perhaps they coincidentally settled on the Apple-specific settings as the corporate standard.) The word-of-mouth I've gotten from the Beige G3 owners I've known generally corroborates the impression of these things being "picky" but your mileage undoubtedly may vary.
This is another area where I've just had terrible luck with the B&W at least. So far I haven't had an issue with video cards but with both network and USB cards that machine has been *way* more picky than a Quicksilver G4. (As in "pull the card that works fine in the G4 out of the G4, plug it into the G3, it causes pain and agony. Works fine again once it's back in the G4.") Again, undoubtedly a "mileage may vary" thing.
The B&W and to a lesser extent the Beige both have a rep for entering strange coma-like states that magically resolve themselves if you, I dunno, unplug them overnight or sacrifice a chicken somewhere in the vicinity. (No to mention actual hardware failures that are common, like voltage regulators in the Beiges and the Firewire module in the B&W.)
All of those machines are picky about IDE drives as well. In both the B&W and the iMac I've encountered multiple cases of drives being recognized well enough to let you install an OS only to find it unbootable when finished. (It's such a joy to be greeted by the screen-filling Ghostbusters-logo-sans-ghost on the B&W when that happens.) Swap in a different brand or model of drive, works fine.
(OS X seems to be a factor here; sometimes the "bad" drives work fine with 9.)