I actualle hate (every version of) AIX, but its journalled file system is fabulous.

For Linux, the question of what makes it a dream OS very much depends on its use. As a desktop it stands and falls with what you require in the Window Manager and I have founs none yet that fulfills all my wishes: speed, easy of use, dwimmery, minimal (but functional) decoration, looks (without bling-bling) etc etc. I stuck to KDE because of the easy key bindings and the possibility to minimize decoration, but it is still slow and starts too many background processes for functions I don't use but without those background processes KDE won't start.

In the end ALL software sucks and will cause reasons for hate.

In Paris (QA Hackathon) I learned that MacOS only supports a very limited set of file systems fr external drives (no FAT32, Ext2, Ext3, or Ext4), which would be yet another reason not to want it (price being the primary reason not to buy a Mac)