A lot of people feel their data is exceptional, and so meta data is where I see "custom" hurt content creation the most: Whereas WordPress has a neatly rolled meta data extensions into "Custom Fields" many CMS degrade into a morass of form fields.
People should be wary of custom built CMS UIs, not only because most people have learned a UI like WordPress or Tumblr.
People should be wary of custom built CMS UIs, not only because most people have learned a UI like WordPress or Tumblr.