Cool.  I'm beginning to think that I will begin to use fewer packages and systems that do not allow integration, customization, and extensibility.  A few applications for Microsoft Windows (especially MS Office) ship with Visual Basic for Applications that allows customization and extensibility by using Automation and COM objects to script custom tools.

Radio UserLand offers a very open architecture complete with an object database and a rendering engine.  It's amazing what kind of underlying horsepower you get for the $39.95 initial price tag.

And, not for the faint of heart, there's always the open source world of applications based in Perl, PHP, Java, etc. that allow customization at a minimum.

But Movable Type is a great example of an application where customization and extensibility is built into the architecture.  That rocks!