Another school of thought is that plants aren't generally damaged by casual overwatering, but that many houseplants aren't thriving because of poor-draining soi

Another school of thought is that plants aren't generally damaged by casual overwatering, but that many houseplants aren't thriving because of poor-draining soil mixtures or being left with wet feet. If you fix the poor soil, you don't need to worry as much about overwatering because they aren't suffocating every time they're watered, creating a perched water table in the container. Peat-heavy mixes also have a nasty habit of going hydrophobic when they dry completely - it can be a difficult problem to fix. A bonzai grower called Tapla wrote a fantastic series of posts on the Gardenweb forums about the importance of drainage in container soils. I'd encourage anyone interested in this stuff to check them out - they've been instrumental in keeping my indoor trees alive.