One hole is as effective as 100, so long as it allows water to pass.

If you were to employ the 'pot-in-pot' technique, it is most effective at removing excess water when the cache pot is also filled with the same soil you're growing in. This set-up "fools" the water in the pot you're growing in into "thinking" it's in a deeper pot than it is actually in, so the excess water moves down through the drain hole into the second pot. However, this method is virtually ineffective at removing excess water if the cache pot is full of large pieces or the growing container is somehow partially 'suspended' in the cache pot.

Al

Al, correct me if I'm wrong on this. What I do with cache pots is to fill only the bottom of the pot with my regular soil, and then I place the actual container on top of this soil, making sure that the soil in the cache pot completely covers the drainage holes of the actual container. I'm guessing this is all that's needed to tricking the pot into "thinking" it is deeper. Then, around the sides between the two pots, I put large pieces of material (large wood chips, usually; packing peanuts might work better) with large air spaces to act as an insulating layer against summer heat and winter cold.

With this setup, I feel I get the best of both worlds: good drainage at the bottom, and insulation around the sides. I was never much good at physics, so is my thinking correct here?

Mmhmm - absolutely. ;o)

Al