If you haven't developed WPF applications before, there will be quite a few things in Silverlight that may be new to you at first. However, even if you have experience with developing WPF applications, there are still a few surprises in store for you.
A good developer works hard to separate logical elements and presentation code. In web development terms, this means specifying your logical elements in HTML and styling those logical elements with CSS. HTML and CSS use different syntaxes and switching between the two can test one's patience. Fortunately for us, separation of logic and presentation is a key design principle in Silverlight, not an afterthought like CSS was to HTML.