I do not think web startups in the launch phase is that much of a niche. There are often times 20 "Ask HN: Review xxx site" posts on here a week and that's just on HN. I'd be perfectly happy with just those 20!
I fully agree that the site owners may not have much reason to return to launchly after their launch is over and they no longer need feedback BUT new launches are constantly happening. A (hopefully) big audience for launches will be web development shops that are constantly putting out client web applications. They would be able to include a launchly launch as part of their "package" to the client.
I think the returning visits will be from the "general audience" that is just interested in seeing the latest web apps and having a chance to give their valuable input... just like people do here on HN.
Thank you for your thoughts!
So, what you've built looks very nice. You seem to have executed well from a technical perspective...but I fear you're about to find out that you don't have a sustainable business (beyond maybe paying for the server costs).
Then again, what do I know? I work on boring stuff all the time, and I thought Facebook and Twitter were kinda dumb. I could just lack the vision to see what you see in this particular niche of this particular market.