The creator of co.mments, Assaf Arkin, a Rails developer, has created a plugin that makes it easy to add a Undo feature to your Rails app. Instead of warning users about things simply let them do it, but give them the choice to undo afterwards. Assaf's plugin doesn't cover all the bases, but it's easy to build upon for creating your own system. For deletion, for example, you'd want to come up with a way to keep the data floating around for a while.