How long is it before you see your ideas posted by others?

Every idea I have someone does and posts to HN a few weeks later if it doesn't exist already. Anyone else suffer from this? I suppose being part of the HN hivemind contributes to this a bit.

*idea: Idea is taken to mean 'good' idea. A good idea is an idea that meets the criteria from PG's "Startup Ideas" article. Preferably, the idea is something you actually wanted to use yourself.

Maybe it really is about speed, and I need to build something fervently as soon as I have the idea...Any suggestions?