OK, after sometime getting used to this new OS, I finally found some weakness as compared to Windows or even Linux GUI. First of all the font rendering. Unlike Windows' ClearType font rendering that is sharp, OS-X fonts are blurry, especially from close distance. Some people on the Internet mention that OSX' fonts look better if we see them from a few feet. Hey, I don't want to work with my keyboard a few feet away from my monitor. How about inevitable built-in laptop screen?
The second weakness is its ability to display true color. Turned out it is not 24-bit RGB. This results much less than 2^24 colors as it supposed to be (my Compaq laptop has true millions of colors. I couldn't find any artifacts/washed out colors when playing movies from DVDs). Don't get me wrong, this issue is only seen on Macbook (or Macbook pro) built-in LCD screen. If we hook up to external LCD monitor, that's gonna be different. I have seen the iMac screen, it is much better.