It's great if your product takes off with the first launch, sometimes they do. Sometimes they don't. That doesn't mean the product is doomed to fail, it may just mean that you have to follow-through. And a lot of people don't.
There was a fair amount of hoo-hah about Bootstrap when Twitter announced it. The usual quick pieces on TechCrunch, GigaOm, PaidContent. Maybe a few posts from bloggers like Scoble or Jeff Jarvis (I don't know if these guys specificially wrote about it). The product rolls through in a wave of publicity and that's it.
But just a half-hour after writing the review of Bootstrap here, weeks after its rollout, I'm getting emails from people who hadn't heard of it, people who could really use it.
No one promoted the product to me, and believe me, I'm not asking them to. But here's what can't possibly hurt. If you're the developer of the product, think of the people you read and whose opinions you care about. Not just who the PR people say are influential. Who influences you? In general those are good people for you to tell about your product. You don't have to write a fancy marketing piece, just an email that says hey, I read your blog and I thought you might find this intereresting. Include a link. Say thanks, and sign off.
For me, products that were made by my readers are inherently interesting. Here's a product developer I know I can influence, who I am influencing. If I see something in their product they're likely to listen. That matters a lot.
I don't think of this as a conversational medium like some people do, because I think that leads to people saying empty things just to "engage" with you, and I prefer to be treated like a human being, not a business model.