GUI: copy it or design it?

I’m a big believer in following the standards for GUI and interaction design. But when do you copy or reuse an existing design, and when do you design something new? Here’s my guideline for when to design and when to reuse or copy the GUI and interaction:

Reuse When… Design
…there is an external standard.
For example: the Vista UX Guide recommends […].
…there is a GUI or interaction precedent in your software.
For example: we distinguish between Import and Open.
   …the precedent uses an out-of-date interaction style.
For example: the users cannot drag an object to move it.
  …the precedent uses an incorrect mental model.
For example: user preferences are saved in a text file.
  …usability tests say the precedent reduces performance.
For example: 70% of occasional users do this wrong.
 …the developer wants to re-use existing GUI.
For example: use a variable to change the dialog-box title.
 …competitors have implemented the feature better.
For example: when they zoom in, it’s smooth, not stuttered.
 …the market has a certain GUI expectations.
For example: iPhone promoted gestures, others had to copy.
  …the product requires a certain strategic direction.
For example: all data must be sharable, locally and remotely.
  …there aren’t sufficient resources to design.
For example: “There’s no time in the schedule for design.”

Reuse your existing design ordesign it using Five Sketches™.
Copy the competitor’s design orleapfrog their design.
  If you ship a feature with poor interaction or poor usability, where’s the user value and where’s your credibility? Not all design processes are lengthy. Five Sketches™ takes about a day for most features that you’re tempted not to design.

Here’s an example: did Internet Explorer leapfrog Firefox?