I was reflecting on my friend and colleague's, John Newton, post about his recent adoption of the Mac. He asked us to suggest which applications he should get (Adium, Handbrake, NeoOffice, etc.) and it got me thinking, "Beyond third-party applications, which features on the Mac itself could I not live without?
Pushed for just one, I think it might well be Expose. Given that through the day I tend to open more and more windows, it can get confusing to find my way back to the one I need at a given moment in time. I use the Dock, yes, but I find Expose the best tool of all for sorting through the clutter to hone in on the application I need, and the window within that application that I need. Invaluable.
If I were given two choices, my second would be the Mac's native support for PDF. It is mind-expanding to suddenly be able to create a PDF from any application. This ends up saving so much time (and money otherwise spent on Acrobat). You don't recognize what a lifesaver it is until you try going without it for a few days/hours/minutes/seconds.
What are your must-have features on the Mac?