What makes OS X a great platform?

Asides from the build quality of Macs and the visual appeal of the OS, deep down there are some great features of the OS which makes the platform great which we take for granted. What I think are some strengths include:

  • Hassle-free program installation process - no running through pages and pages of installation steps; also the Mac App Store provides 1-click installation
  • Can increase hard drive partition size without reboot (probably a UNIX feature)
  • Excellent foreign language character input e.g. Chinese (Windows 7's is not as good)
  • Good visual window management with Application Expose
What else can you think of?