Yet the nature of m-commerce transactions, most relatively small in size and concentrated on items that are time- or location-sensitive, will limit the overall size of the m-commerce market.

ECONOMIST: Waves of the future

You can choose what services to use with Google Now, so if the idea of Google parsing your e-mails sounds like an invasion of privacy, you can limit it to just Web history and location information.

CNN: Google's predictive search comes to iPhone, iPad

But even for solar, the vicissitudes of the sun (which vary by season and location) and the diffusive nature of solar power limit its potential.

WSJ: The Experts: What Renewable Energy Source Has the Most Promise?

If you prefer to limit your Houzz to photos of rooms done by designers in your area, you can filter by location.

WSJ: The Digital Solution: Professional Decorating Ideas in the Houzz