I haven't done any WP7 dev (but would like to). However as I understand it, WP7 applications target .NET Compact Framework 3.7, and support a subset of Silverlight 3. Therefore I don't think this library would actually work as it stands now since
you are using some .NET 4 specific methods. Also for example the encoding library includes a Windows Forms control which references the System.Windows.Forms namespace. I don't believe this would work on WP7, but I'm not sure.
I think if that's your real goal you should consider the way the solution is set-up as well. Maybe consider splitting out the encoding library into several smaller projects. For example, move the rendering control to a separate windows
form library, a separate ASP.NET library and possibly a WP7 library as well with the core encoding library being non platform specific. For example, you could easily take the bit matrix from a qr code and write platform specific rendering code. Provided
the core library is using the lowest common denominator, that is to say CF 3.7 features than it should be compatible with all target platforms.
Also I don't believe you'd actually want to create a WP7 app that generated a QR code, you would only want to read/decode QR codes from a phone right? Therefore it doesn't make sense to have the rendering code in the core library or targeting WP7.
These are just suggestions, I hope they make sense and help. If I can contribute to the project in any other way I'd be happy to do so. Like I said it's already a great library at this early stage. My suggestions are intended to help you
reach a larger audience of users.