Data Access Layers and LINQToSQL

I've been starting to do some thinking about application architecture, more specifically Data Access Layers and LINQToSQL.  Some of the things I've read, or mean to read are "LINQToSQL-The Data Access Layer Shrinker", MSDN on "Flexible Data Access With LINQ To SQL And The Entity Framework", "Creating a Data Access Layer" Part 1 and Part 2, LINQ Samples, "Build Your Own Data Access Layer" series and "Building a Multi-Tier Web Application in the .NET 3.5 Framework Using LINQToSQL".