Thanks to those who responded to my post on hitting the curve, or cliff as PsiSpace put it.  Please keep the comments coming...

Two additional thoughts.  The first is one that Darren David made in his presentation on building the North Face Prototype he gave at MIX (which should be available to the public at Virtual Mix shortly).  His recommendation -- which I agree with -- is to dive in with the knowledge that you will rewrite your first application.  Just get it working and know you will go back and rearchitect.  Don't be afraid to get your hands dirty even if you have this intuition that you aren't "doing it the right way."  Just do it knowing you'll revisit the code.

The second is what comes after the curve: performance.  That's where a lot of people seem to be right now that I am working with.  They've written some pretty sophisticated code and complex applications. Now they are wanting to optimize.  Well, what do you know: Tim Cahill -- dubbed the "WPF perf guy" -- is now blogging.  And he is blogging fantastic stuff.  Once you've hit the curve, go live his blog.