I sent an e-mail to Don Box asking if the collections API in Whidbey will have Ruby-style iterators over collections, to go with C#'s new support for anonymous methods (aka closures). His entire reply: "Yes it does."

Holy crap... between generics and this, the collection classes in Whidbey are going to rock. I can't wait to do this:

List<Employee> employees = ...
List<int> employeeIds = employees.Collect(delegate(Employee e){return e.Id;});

Now if only there was a C# IDE that could keep up with IntelliJ...