I've written a tutorial on how to implement Perlin Noise in both a pixel shader and a vertex shader. The tutorial is available over at Ziggyware.
Check it out! I welcome any feedback.
I found out I have won first place in the Ziggyware contest! I'm very happy that my first XNA tutorial was such a success. Perhaps I will write up more in the future.
It appears that Ziggyware no longer exists, so I have shared the article, screenshots, and sample code on my server. You can download it all here: