This is definitely a hard problem for solo developers who are like me and have significant difficulty with social aspects. I've never submitted any of my projects or writing here, because I have this underlying feeling that I'd be bothering people. It also doesn't help to be on a site filled daily with dozens of really incredible projects that feel so much more deserving of attention. Yet I've often found myself bewildered by concepts such as SEO and promotion, and I much prefer to spend my time coding. I hate to generalize, but I can't imagine I'm particularly unique in this regard.
But indeed, it's a serious growth limiter when we are stuck working alone. I feel like any serious open source project really needs someone on the team who groks all the social stuff and can get the word out to the right parties who would be interested. A networking service to connect these two types of people would truly be invaluable, I feel.
I was also told that technical writing helps a lot, and indeed, despite being a little guy in a small niche, two of my articles were submitted by others recently, and seeing such a positive response has been a huge boost to my self-esteem and confidence. (It did ruin my bounce rate stats though, went from 44% to 87% in two days :p)
But yeah, I'll agree with the arXiv conclusion that HN is an incredibly valuable resource for open source developers, with a very friendly community behind it.