Tabbed browsing and other efficiency enhancers have existed for many years from third parties, so I'm happy to see Apple finally implement them. That being said, Mac OS X has been pretty solid in recent incarnations for the past several years, but newer trends seem to be going towards abstraction and minimalism. Mac OS X has generally had an upper-hand with regards to intuitive usability, but I do fear the "future" trend of such abstraction will lead to a lack of intuitive usage, as well as further hiding of usable features.
But I suppose that is the flow and nature of maturation of user interface. One has to eventually keep up with the unspoken rules of user interface (such as decades ago, needing to understand "new concepts" such as double-click and point-and-click, etc.), sooo I suppose I am not really complaining. But the nature of human boredom is quite sad, in that the most efficient and usable UI- if ever conceived and implemented- will ultimately have to be replaced due to users feeling their system is aging, if OS remained relatively unchanged.
So here's to the idealistic Mac OS-- may I use you in the future that will never come.