There are a ton of "startup directories" like Product Hunt that list new startups and apps.
Is it worth the time to add your new startup to all these sites? Due to the large numbers of companies that launch each week, it's very hard to make your site stand apart to begin with.
Hacker News, reddit, Product Hunt, TechCrunch and other startup directories are not particularly useful to gain actual users. You want to make some noise where your potential users are.
A successful mention on one of these sites will bring you a spike in traffic, but it will be short-lived and you'll be disappointed by the conversion rates. Most people are curious to find out about new startups, who you are, etc. but they couldn't care less about using your product.
So yes, spend 5 minutes when you "launch" to post on those sites, but do not make that your launch strategy. Focus on finding a repeatable way to find targeted potential customers.
Your first priority should definitely be getting traffic from your target market.
That said, getting listed on Product Hunt and other directories:
Is it worth the time to add yourself to all of these directories, or to craft a launch strategy around them? No. But it's low-hanging fruit to simply submit to the ones that are self-serve, and ask a few friends to consider up-voting (ping me, @JayNeely; I'll take a look).
If you flop, it's cost you nothing. If you get clearly accurate feedback ("she's right, that phrasing is confusing"), it's already worth the (non-)effort. If you get demands for specific features ("I'd never use this unless it had ____"), thank people for their feedback / let them know you hear it, but wait to hear it from your target audience too before spending time on it.
Let me know if you submit to Product Hunt, /r/startups, or Hacker News. I'll take a look and upvote if you look good.