In practice, we've been using DCI (with object.extend) in a production Rails app and have seen no worse performance degradation than in other apps with comparab

In practice, we've been using DCI (with object.extend) in a production Rails app and have seen no worse performance degradation than in other apps with comparable complexity (at least subjectively--of course it's very difficult to measure objectively). Typically plenty of production apps suffer more from simple things like missing an index on a db column, N+1 queries, iterating over objects in Ruby, or poorly-thought out design. DCI in Rails is a pretty good trade off for when you need to use it.