rolf wroteIt says it provides an easy way to start coding yet I know how to set up LAMP and nowadays it's pretty easy anyway. I think it will just bring a layer of opacity into my environment, so I'll pass.
I think you're missing the point here. WebMatrix allows you to work in a PHP or .NET environment. Plus, by installing the web helpers, a lot of the tedious tasks can be done in one line of code. Example:
@Twitter.Profile("Microsoft");
This will provide you with a fully customizable twitter feed. There are also other web helpers for displaying WebGrids and many others. And trust me I know these could be very helpful when coding because there's a similar concept of HTML and AJAX helpers in ASP.NET MVC. Those helpers would allow you to focus on the stuff that are exclusive to your website/application (your business model) rather than having to deal with all "accessories".
In addition to that, I've read a tutorial on using WebMatrix that shows you how the framework helps you to create SEO friendly website and sync your development and production environments (using Web Deploy).
I still cannot provide a full review on WebMatrix because I've just got to know it today. Maybe someone who used WebMatrix before could tell us whether it's worth it or not.