Mac OS X, like iOS, has the ability to grow upon you due to its painfully perfected visuals and tools. I mention a few of these below.
Windows 7 has borrowed some of its ideas and so has Ubuntu, but the Mac OS X dock just blows you away with its fluidity, sharpness and utility.
The App Store
Just like iOS, Mac OS X now has an app store with several paid and free apps. This is such a huge convenience - you just have to go to one place to look for apps. You can also trust Apple to do due diligence so you know an app will not harm your Mac.
The Viewer along with the Writer app can be used to view several common file types. One feature of the Viewer, that I particularly like, is the ability to join PDF files. Just drop PDFs on top of another PDF document in the Contact Sheet view and they are joined. Save as a new PDF document when you are done.
The not so awesome things
Mac OS X does not come with a native image or photo editor. Fret not, there are several free and open source alternatives. I particularly like PaintBrush. It also does not have a text editor but TextWrangler from Bare Bones Software is a nice free alternative.