People love to talk about themselves, and they love to gripe about what's broken and annoying, so it's much easier than you might think. Finding problems to solve is actually extremely easier. The harder art is doing the follow up to understand if there's a good business model for someone who solves the problem.
Many of these niches are technologically very simple. e.g, there's someone I used to talk to online who makes a software package for manufacturing that consists of little more than basic geometry and a good UI. To a customer base that hates math and needs to do certain calculations frequently, that $29.95 program is perfect.
If you ever spent time in a mid or large sized company and talked with people in various departments and what sucks about their day to day tasks, then ideas are abound (or as previously mentioned, make friends with people who work in such environments, and pick their brains about what sucks). PMs have their pain points, sales guys have their pain points, IT guys have their pain points, etc.