<p>As someone with some winforms and client applications experience - is it worth going back and learning the way traditional ASP .NET pages work, or is it okay with moving straight into ASP .NET MVC?</p>

<p>I'm kind of looking for pitfalls or traps in my knowledge of general C#, that I won't know from the screencast series and things on the ASP .NET site.</p>

Here is the great thing about MVC. It works closer to the base of the framework than normal ASP.NET Web Forms. So by using MVC and understanding it, you will have a better understanding of how WebForms work. The problem with WebForms is there is a lot of magic and about 6 years of trying to make the Web work like Windows Forms, so you have the control tree hierarchy and everything translated to the Web. With MVC you get the core with out the WinForm influence.
So start with MVC, and you will easily be able to move in to WebForms if needed.