I know the System.Tuple type in fx4.0 (http://msdn.microsoft.com/en-us/magazine/dd942829.aspx)  will be useful and glad it was added.  But if you had to make an argument for why you need it over creating a property class (e.g. DTO), what would the arguments be? Reducing number of classes is one (program size and complexity).  Having to stop and define a new type is another (programer speed).   However, having a concrete type can also be an advantage.  Please weight the pros and cons.  tia.