LINQ to SQL Obsolete

According to Oct. 2008 blog posts by Lead Program Manager Tim Mallalieu, Microsoft is making significant investments in the Entity Framework such that as of .NET 4.0 the Entity Framework will be the recommended data access solution for LINQ to relational scenarios.
Applications built on LINQ to SQL will continue to work but might not benefit from future Microsoft technologies. However, migration from LINQ to SQL is manual, and developers might want to wait for the next version of the Entity Framework before migrating.

Technologies overview:
LINQ:
The Language Integrated Query (LINQ) is a set of APIs and programming language features that enable data access queries to be written in programming languages such as C# and Visual Basic, rather than treated as text data. LINQ simplifies data access code and enables the developer to use the Visual Studio tools, such as the compiler and IntelliSense command completion, to help write queries. At its launch, LINQ supported a variety of data sources, including in-memory data objects and XML documents, and the Microsoft C# team had built a stopgap LINQ connector to SQL Server—LINQ to SQL

LINQ to SQL:
LINQ to SQL enables application access to SQL Server via LINQ, a feature of languages such as C# that simplifies data access coding

Entity Framework:
More general data access technology that provides LINQ connectivity to SQL Server and other database management systems, including Oracle and IBM DB2.

LINQ to SQL and Entity Framework Story:
LINQ to SQL debuted with LINQ in the .NET Framework 3.5 in 2007. However, when LINQ to SQL shipped, the Microsoft data access team had already begun work on the ADO.NET Entity Framework. When the Entity Framework was introduced with the .NET Framework 3.5 SP1 in July 2008, LINQ to SQL became largely redundant.