I have found LINQ to SQL and the Entity Framework has a few missing features, one of these is the ability to update the designer diagrams, and this is where Huagati DBML come to play.

Huagati DBML/EDMX Tools is an add-in for Visual Studio that adds functionality to the Linq2SQL/DBML diagram designer in Visual Studio 2008, and to the ADO.NET Entity Framework designer in Visual Studio 2008 SP1.