I don't think professional devs with existing experience in ASP.NET are really the target of WebMatrix.
Now IIS Express (also released today), that's something that's interesting to me.
I installed IIS Express Beta on my Windows 7 Professional laptop a while ago, but it just ended up confusing me. I don't know how IIS is hosted, where it exists, how it runs, and how it interacts with the 'real' instance of IIS on my computer; things like shared configuration and whatnot.
For now, I think I'll stick with the IIS and SQL Server running within a VM combined with Remote Debugging.