Open Source Doesn't Just Market Itself
Your project doesn't market itself, but remember, many folks writing open source really don't care if anyone else uses it or not.
The statement, "But if you believe your project has value — which you probably do, since you spent time on it — you should try to get it in the hands of as many people as possible," is not really true. There are times it makes sense to market it widely, such as: 1) you are a consultant and want to use it for marketing yourself, or to get gigs based on it, 2) the project complements your product so driving wider adoption of it has positive implications for your main focus; 3) you are attempting to establish a name for yourself via open source, and being an author of a widely used library is a Good Thing. There are others, but those are three common ones.
There is a VERY large class of open source where this just doesn't matter though -- things which you write for yourself to use, which solve your problem, and which there is no overhead to open sourcing, so you do it altruistically. Frequently, in this case, adding lots of user support, community building, marketing effort, etc will in fact add enough overhead that the project becomes a net negative in relation to your goals.
This pretty much sums up why I made a Shamwow inspired commercial for my project (RestSharp): http://news.ycombinator.com/item?id=2460298
I also had stickers made that I mail to contributors and promoters. If I had the cash, I'd make tshirts. All of this makes the project feel vibrant and alive which inspires people to participate and contribute.
I used to think that marketing didn't matter then I realized it does matter. Now I'm realizing that it doesn't matter again and that it's just another way that the profit motive seeps into the project and starts making it un-fun.
Marketing a free software project is the same as SEO: have good code and documentation and you're 90% of the way there. Most projects don't have very good documentation, or they actively discourage users and developers in other ways.
Make it easy for people to use and develop the project and you're ahead of the game and don't have to worry about marketing or any other bizniz development crap.
The Changelog[1] does a pretty good job at telling the world about awesome open source projects. Especially their new gig at the github blog (github reflog[2][3]) is always worth checking out.
No, but it tends to be marketed by the same people who made it. Much like Bob the discount furniture guy[0].
The case of Bob is particularly interesting to me. Back in the early nineties Bob commissioned a slick marketing campaign with trendy music and hip radio personalities. I surmise it didn't drive sales too well because it lasted for only a few months before he dropped it and appeared in his own commercials, in trademark polo shirt and jeans with his loud annoying voice. The authenticity, real or perceived, helped turn Bob's from a Connecticut business with a single location in Newington into a force to be reckoned with throughout New England.
It's true, I've recenlty found some interesting open source projects while browsing Google Summer of Code accepted organizations.