Whenever i'm leaving the house, be it for traveling or just going to have a haircut, i can't help but thinking about current and possibly new online ideas. (Foreign) newspapers and magazines most often contain nuggets of information for a potential and untapped online project.
As an example, a couple months ago during traveling i stumbled across a business magazine article about new hospital multimedia systems and found the keyword 'bedside terminal' interesting enough to build a site (no blog atm) on it .
In general, i think micro niches can be found in upcoming markets, new products and services etc. The trick is to identify these before they hit the web and create an online position before anyone else does. It may involve some speculation too but on the other hand, calculated risk is already part of our business.