I've connected with some fascinating people from HN, maybe 1/3rd of the time people write to me and 2/3rds I write to them. Had some really cool conversations, got book recommendations, talked about projects, lots of good stuff. Sometimes a person doesn't have their profile filled out and you have to dig through the comments and submissions hoping they submitted their own site or posted their email. Sometimes even after that, there's nothing there - then you've got to try to google their username. Nothing there? Well, no dropping them a line then.
That sucks - you'll miss out on meeting some cool people. Take the 20 seconds to put an email in your profile or a website that you run.