This is exactly what Steve Jobs would tell me every week when he would look at the latest Finder build. Of course, we needed multiple pieces of infrastructure to get there; a journaled and indexed filesystem, kernel-level, file system modification notifications, metadata indexing systems, etc. All of the pieces did appear, but there are also those darn stubborn users who kept insisting on the ability to navigate a physical file system to an actual file.

Many of the features of OSX (which I rarely use, but worked tirelessly on) came as a result of Steve's dislike of having to know where files were and having to navigate to them. The Dock, Spotlight, Mission Control, Expose, even Time Machine all came out of Steve's hard-to-pin-down concept of what a modern user interface should be.

I suspect it may be possible to create a fully "Smart Folder" query driven Finder experience. Your sidebar could be populated entirely of saved queries. This might be a fun experiment!