For the past years of my career as a .NET developer, i can hardly remember that i used interfaces as parameters or return types from my business objects. DAL interfaces are out of this context since you want your DAL methods to be generic for whatever datasource. For those two years, I am really a fan...

I have this custom layout logic for a custom container control which uses a number of properties defined on an interface implemented by most of our controls. For this implementation, I needed temporary holders of controls which implement the said interface and the need for an array of the said interface...