This captures something I've been thinking about for a while, it seems like there's about 1 or 2 life-changing apps/services a year.

Dropbox fundamentally changes how I collaborate with non-coders, makes it somewhat more like version control.

Instapaper changes how I browse and work...much less tabs these days and less "interruptions" from new content.

Spotify means I never have to micromanage my music collection again, or even worry about all these cloud music hosting services.

It's not for every startup, but the potential to change ways of life is definitely a good litmus test for an ambitious startup.