Thanks to your excellent tutorial I was able to migrate your Python implementation to C#. I am running mono on the Raspberry Pi and using RaspberryPi.Net library.
You can find his code here. From the software documentation:
The purpose of this library is to provide a Mono.NET interface to the GPIO pins on the Raspberry Pi. All of this code was written using Visual Studio 2010 Express but the goal is to be fully compatible with Mono. This library is written using .NET 4.0 therefore the latest version of Mono (2.10) is recommended. At the time of this update, the Raspbian wheezy 2012-07-15 image installs Mono 126.96.36.199.
The GPIO pins are best described here. They can be accessed in 2 ways, either using the file-based I/O (GPIOFile.cs) or direct memory (GPIOMem.cs) using Mike McCauley’s BCM2835 library which is available here. There is also a GPIODebug.cs class that can be used to test your application without a Raspberry Pi.
Here is a sample bit of code to blink an LED attached to pin 12
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