Sleep sort with Reactive Extensions

SleepSortWithReactiveExtensions.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reactive.Linq;

namespace RxHello
{
    public static class EnumerableExtensions
    {
        public static IObservable<T> OrderBySleepSort<T>(this IEnumerable<T> xs, Func<T, int> keySelector)
        {
            return xs
                .ToObservable()
                .SelectMany(x => Observable.Timer(TimeSpan.FromMilliseconds(keySelector(x))).Select(_ => x))
                ;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Press Enter key to quit...");

            var words = "Reactive Extensions give a great power to programmers who deal with asynchronous operations.".Split();
            words.OrderBySleepSort(w => w.ToLower()[0] * 10).Subscribe(Console.WriteLine);

            Console.ReadLine();
        }
    }
}