After owning my Macs for a while, and after more time behind the wheel of OSX, several these stood out as 'wow' features, and a few annoyances arose too.

• stuff just works when you plug it in…printers, cameras, camcorders, MP3 players, thumb drives, mice.
• no reboots except when updating the OS
• no DLL conflicts
• no driver hassles
• very simple software installs
• automatic updates with no “Windows Genuine Advantage” hassles
• all the cool stuff comes with each mac - iWeb, iMovie, iPhoto, iTunes, iDVD, and Garage Band
• intelligent use of a dual-core processor (one is dedicated to the graphics core)
• Open Office and NeoOffice provide a free MS Office compatible office program
• OSX has all the advantages of unix, with a pretty face to boot
• no cheesy demo software or nagware when you buy it
• extremely quiet (if the monitor is in power saving mode, you won't know the machine is on)
• nice parental controls
  • restricting hours of use (i.e. 9am - 8pm)
  • limiting computer time (i.e. 2 hours per day)
  • restricting web access to certain sites
  • limiting email communication to an approved list
  • restricting computer use to authorized programs (i.e. no web chat for you!)
• my kids can do stuff without help, like:
  • create movies with credits, title screens, transitions, etc..
  • create songs using drum and guitar loops, keyboard sounds, etc..
  • take pictures of themselves
  • burn CDs of their music and schoolwork
  • make DVD movies (yes…good ones with custom menus, navigation, and more)
  • surf the web and use email safely
  • do their book reports with clip art, fonts, etc.. and print them to a network printer

These are all minor points for most users, but they're important to me…

• iTunes builds separate music libraries for each user. My wife and I share the same machine, so wouldn't it makes sense to have a shared iTunes folder for both of us? You can do that by setting each user's music location to the same location on the disk, but iTunes doesn't auto-detect that another user has added music to the library and update my music list. That should be an administrative option.
• iPhoto has the same problem.
• iWeb reminds me to buy a .Mac account each time I create a web project. Just make ”.mac” the default selection when I run the new project wizard, but give me other choices. (**Note: this issues has been resolved with iWeb '08. Funny, it works exactly like I described here, only it prompts you to publish when you exit the application rather than when you create a new site).
• The default key bindings are awkward. Support for different key bindings like BRIEF, EMACS, Windows, etc… would be easy to implement and would have a huge impact on most users. Putting this in the personal section of the System Preferences application would be a no-brainer.
• Apple's Java support is minimal. This doesn't affect most people as much as it does me. Apple released a Java 6 VM more than a year late, and it only supports newer 64-bit processors (what about older Macs running Leopard?). I wish Apple would throw their support behind the Open JDK project (here) and let everyone reap the rewards of collaboration.