I'm always surprised by people who can't think of an idea to work on. My problem is I start on one and then get distracted by the next one too soon. I've got a jar of post-its with ideas of varying strength.

Maybe these people don't count the silly ideas they get, which they have no way to solve, or would not actually produce money, or are impossible.

Fair point, but I suspect the "Need an idea"-types (to generalise) are looking for anything that might have a faint hope of success. If you have the judgement/sense to discount ideas for the reasons you listed, I doubt you're on HN begging for ideas.

I have gone a little step further and actually implemented them. Then no one came.

My new pet is heavily quantitatively researched. Had my first 5 users before I even mocked it up. I just sent them something I made in mockingbird for their review, and they don't seem to be involved in software development (they're all academics/artists and are giddy about the experience :-)