"Think Of" and "Think About"

Concept: When we think of something/someone it is a passing thought, not deep and analytical. When we think about something it is a sustained period of reflection on that thing.

For example:

Think of - have a thought - example - "I thought of you on my way to work." 

think about - consider - example - "What should we do? I don't know. Let's think about it. (We'll consider the possiblities.)