I've been asking around and I hear the same thing over and over again from people/startups/companies that list their positions in the HN Who's Hiring: applicants are putting zero effort into their emails.
Just in the past hour, I have personally received 8 responses for a business development position that were simply "Hi, saw your listing on HN, here is my LinkedIn. Call me."
Guys, this kind of email does not get you hired. It will especially not get you hired when your LinkedIn profile is set to super private and the only thing I see is your picture. Even worse is when you don't even bother to send an email to the poster directly and it's instead just BCC all the emails in the Who's Hiring thread. And even worse is when you apply for a position that's not even the one being offered. Take the time to actually read the posts: just because a listing contains the word "developer" does not mean it's a software developer. Business Developer != Software Developer!
Some friendly advice: if you at least click on the links in the posts, take a look at the startups' sites, and just mention in your email "I see your product/service X, and think it's interesting" the value of your email and the chances of getting contacted in regards to the job shoot up infinitely more.
HN Who's Hiring is not CraigsList. It's mainly quality people posting because they know there are quality readers looking to get hired. Put a tiny bit of effort into the emails you throw out, it's an investment that will pay back greatly! Remember, this is the first impression you are making on someone who might be your future employer! You're often not dealing with HR staff/agencies, and will be likely directly in touch with the person you'll be working with/for should you be hired. Show some effort, make it look like you at least care.
Yes, it's not easy to sit there and read about each of the companies and what they're working on, but it is a hirers' market and if you don't show the initiative and stick out as someone who is earnest about becoming a valuable member of the team, why would anyone bother replying? Especially when startups are looking for the top talent (whether they need it or not is besides the point), HN is full of A-list developers/founders and A-listers only hire other A-listers. Your "meh, here's my info, you do the research about me and if you're interested call me up" is not the kind of attitude that inspires confidence and will not get you a job.
I know for a fact that HN is chock-full of quality talent both hiring and looking to be hired. It is sad that this is the sort of response people posting job listings have been getting. For the sake of the entire community, put a little bit of effort into your email shots. It's better (and is a smarter investment) to look through the listings, get a feel for what companies are working on stuff that would interest you, and spend a couple of hours drafting 10 personalized emails explaining why you are the answer to the question than to simply ctrl+f "developer", ctrl+c, bcc, ctrl+v, rinse, repeat, send.
tl;dr if it'll take the company more effort to reply to your email than you put into sending it, you're doing it wrong.