Josh Kopelman talks about categorizing startups as Saving Time or Killing Time.

I put this in the context of minimum awesome product -- either it should be fricking useful or fricking fun.

Useful means people will pay for it with their time or money. Examples: LinkedIn, Pandora.

Fun means people won't be able to stay away from it. Examples: Pinterest, Angry Birds.

In some cases like Instagram or Flipboard, the product both saves time and kills time. They are both useful and fun.

Lately I'm finding Tumblr to be both useful and fun, too. That surprised me, because my account laid dormant for years until 2011.

On Tumblr, time just flies...

I wonder if different types of people (e.g., spock vs kirk) naturally gravitate towards innovating in "save time" vs "kill time".

Absolutely.

We each have our own proclivities.

I'm a timewaster.

I know other people who were born to make things productive and efficient.

I believe the timesavers and timekillers need each other.

Another (less elegant) way to think about it is to say that people are more willing to pay for things that save time and more willing to give their attention to things that waste time, and therefore the economics change in each one.