Happened across this - Apple Human Interface Guidelines, along with having the standard instructions for developing a product that looks, well… Apple-y, has some great content in their Characteristics of Great Software section.

When making design decisions regarding features in your application,
it’s important to weigh the costs, not all of which are financial,
against the potential benefits. Every time you add a feature to your
application, the following things can happen:

  • Your application gets larger.

  • Your application gets slower.

  • Your application’s human interface becomes more complex.

  • You spend time developing new features rather than refining existing features.

  • Your application’s documentation and help become more extensive.

  • You run the risk of introducing changes that could adversely affect existing features.

  • You increase the time required to validate the behavior of your application.

Choosing
appropriate features and devoting the needed resources to implement
them correctly can save you time and effort later. Choosing poor
feature sets or failing to assign appropriate design, engineering,
testing, and documentation resources often incurs heavier costs later
when critical bugs appear or users can’t figure out how to use your
product.

The following sections present several additional factors to take into consideration before adding features to your product.