IEnumerable vs. List

IEnumerable is less feature-rich than List and also defers some processes until they are needed. http://stackoverflow.com/questions/3628425/linq-ienumerable-vs-list-what-to-use-how-do-they-work suggests that it may be wise to jump through some LINQ hoops while keeping a collection in the IEnumerable shape for performance before poping the IEnumerable off to a list with .ToList()