I often answer questions based on what the run-time (System.Data.Linq.dll) supports, sometimes realizing only later that the run-time feature may not be supported by the visual designer in Visual Studio. Some of these are supported by the command line SDK tool SqlMetal.exe while others are supported by neither tool and require writing code (in C#/VB code editor in VS hopefully :-) )
Feature supported by designer but not by SqlMetal
Features supported by SqlMetal but not by the designer in VS (for most cases, see SqlMetal /? output)
Key features supported by neither design tool but supported by run-time (i.e you have to use code editor and write code the old fashioned way)
I am sure I am forgetting some detailed ones in each category. OK, so please help me make the lists better!