That HN post and a single TechCrunch article were the only things I had to go by in June of 2012 when I applied (and joined) their 3rd cohort. It was an experience that changed my life and gave me the skills and confidence I needed to begin a career that has enabled me to support my family in a way I could not before. I'm sorry to see that it won't be available to more people.
This. I've been using it for a couple of years (old version, no timer) and it has saved me so many times from being frustrated later that I missed a scene in the credits.
akulbe has hit a couple of important points. Just because someone thought of something, or even made a thing, doesn't mean they own the idea. If you copy their exact execution, shame on you. Otherwise, go for it. On paper, any social network is the same thing. But we don't use friendster anymore.
IF it seems appropriate to give credit to someone else for inspiration, go for it.
Just remember, the market will determine the winner. Effectively, that's really all that matters.