We change the database schema, and the code, mostly ".to_f" > "to_d" (and sometimes the developer forced that to make sure of the type even).
Good answer 
A harder one now : What do you think about the whole architecture, to be more precise, about the fact that everything runs inside resque workers leading to potential race conditions, and unexpected behaviour ? Did you make any changes to the way things run and the order in which they run ?