This is really nice. As a nearly-complete newb, I can see how some people find some of the steps hard to follow. For those, I suggest taking plenty of time to look up in the Help starting with the first thing they have trouble following and play with it a bit to get familiar with the terms and Paint.Net features. It just goes with the territory, drawing/painting is like learning a whole new language, and you have to get the basics down before you can even follow intermediate instructions.
Secondly, how would I go about making an "inverted" version of this, the purpose being to create a web button that looks like it is indented, actually pushing down on the button? $20 bucks for a good Paint.Net tutorial that does that?
Also, your button looks a little 3D, like it's got a depth of a couple millimeters, how would one go about making it look a little deeper/taller?