One thing I've always wanted to do -- but have never had the energy for -- was to run multiple implementations of bitcoin (e.g. btcd and bitcoin core) and only transact while they are in agreeance.

For most bitcoin businesses, a few hours of not processing deposits/withdrawals is actually not a big deal, and happens pretty regularly anyway (for no fault of bitcoin itself). While on the other hand transacting after an accidental chain-split could really be devastating.