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 […]

A sketch must be disposible

The strength of sketching is that it’s a fast way to capture ideas.
Since a low-fidelity sketch is fast—pen on paper, as shown—it’s also low cost. And low cost means it’s relatively disposable if it turns out you can’t use that idea.
If you don’t like my first 5 ideas, that’s OK. I can have more ideas, […]