Control the led intensity with a potentiometer that controls the duty cycle of a PWM port.
using System;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using Microsoft.SPOT;
using Microsoft.SPOT.Hardware;
using SecretLabs.NETMF.Hardware;
using SecretLabs.NETMF.Hardware.NetduinoPlus;

namespace NetduinoPlusApplication1
{
    public class Program
    {
        public static void Main()
        {
            PWM blue_led = new PWM(PWMChannels.PWM_PIN_D5, 100, 50, false);
            AnalogInput pot = new AnalogInput(AnalogChannels.ANALOG_PIN_A0);
            double pot_value = 0;

            while (true)
            {
                pot_value = pot.Read();
                Debug.Print(pot_value.ToString());
                Debug.Print(pot.Read().ToString());

                blue_led.DutyCycle = pot_value;
                //blue_led.DutyCycle = .9;
            }
        }

    }
}