Have a read through K. Scott Allen's excellent post here:
And Equality for All ... Anonymous Types
The short answer:
Turns out the C# compiler overrides Equals and GetHashCode for anonymous types. The implementation of the two overridden methods uses all the public properties on the type to compute an object's hash code and test for equality. If two objects of the same anonymous type have all the same values for their properties – the objects are equal.
So it's totally safe to use the Distinct() method on a query that returns anonymous types.
