What exactly does learning Silverlight entail that differs from learning any other .NET environment? XAML is just an xml markup. I only used it on a WP7 app and it took me a couple of hours to get the gist of how it works.
Not much really, especially if you limit the XAML to basic layouts. If you do everything in C#, it's not too much different from something like, say, WinForms. Which is why people like it.