> Ah, I think I'm starting to understand.  While a ground plane provides
> nice shielding and power distribution, "bypass caps" should be wired
> directly across the pins of the IC they are bypassing, rather than
> between
> a power pin and the ground plane (even if the ground pin of the chip is
> relatively close by.)  This helps prevent the transients that are
> produced
> by the chip from being propagated onto the ground plane via the
> "infinite
> resistor array" effect that Dave mentioned.

Right.   I try to locate my caps at the chip ground pin, and I route
thin to the cap, and thick to the chip.


> Even if you directly wire caps to pins,
> EAGLE will happily fill in the ground plane as well.  I guess it
> falls out
> nicely on 4-layer boards, where the inner layers are power planes but
> the
> outer layers (and the caps and their wiring) are on the outside.

I watch where the planing is happening,  and either use "no plane"
zones (old dos orcad) or I move the traces around to prevent the plane
from going where I don't want it to.
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