Differences when using IEnumerable and IQueryable as a type of ObjectSet

Question

As I understand it when I use LINQ extension methods (with lambda expression syntax) on IQueryable that is in the fact instance of ObjectSet they are t

Answer 1

You are correct about IQueryable. As for IEnumerable, it would hit the database immediately upon assigning IEnumerable user.

There is no real difference between using Linq Extensions vs. syntax in the example you provided. Sometimes one or the other will be more convenient (see linq-extension-methods-vs-linq-syntax), but IMO it's more about personal preference.