The one example that most folks know about is Dropbox, where pretty much everyone hated on the original post that Drew submitted. And we all know where Dropbox is at now.
What are some other examples of HN hating on an idea and then it turning out to be the next big thing?
I'd also have to disagree with your "everyone hated on Dropbox"; you can read the original thread at [1], many people said "wow, great!" That's actually the majority of the comments, and BrandonM's comments (which is what people usually refer to) is a lot more friendly and nuanced than "hating on the idea". After Drew's response, BrandonM's response can essentially be summarized as "right, I see how this would be useful".
Like I said: HN is lots of different people who disagree on essentially everything.
https://news.ycombinator.com/item?id=8863