Once again Daniel Dilger provides those of us who weren't at WWDC '08 with more information than we already had, this time regarding new features in Mac OS X 10.6, a.k.a. Snow Leopard, most of which won't be evident to the end user, except in terms of peppier performance and more efficient disk usage.
He even manages to give Microsoft credit where credit is due, for pioneering Fast User Switching, XMLHttpRequest, and innovative text processing features in Word.
Based on what he adds to what was already generally known, I'd characterize Snow Leopard not just as a code refactoring, but as a build-out of features that already existed in some form, sometimes accomplished by moving feature support developed for a particular context into the system where it will be generally available, much as was done with Cover Flow in Leopard, and sometimes by fleshing out support that already existed in skeletal form. Whatever feels half-finished in Leopard should be ready for prime time in Snow Leopard.