I lauched my app over a month ago (
http://www.moreofit.com). I slapped on Google Analytics to monitor traffic amount and sources, and submitted my site to Google Webmaster Tools, which has indexed several thousand pages so far. (I also suggest you use mouseflow.com to view you user's mouse movements and actions). It's fun to see traffic steadily increasing. For the past 3 weeks, each day will usually be a personal record for most amount of visitors in a day. Lately, I've been doubling my daily traffic every week. Of course, it's not possible that will keep up, but I consider it a personal success, considering how close I was to ditching the project all together.
However, still not a single feedback. And my CTR is horrid. And hardly anyone uses the really cool features that I thought were most interesting (eg: filtering by tag, modifying tag importance, etc). Most people just search for something "sites like zamzar", find my site in Google results, find a result (or a few) that they like, and go on with their life.
To answer your question, it's really a personal or relative question. I'm happy knowing that more and more people use my tool to somehow make their life better. Even though not a single one of them thanks me, and they hardly ever click on my ads, I'm OK with that. Probably, it's because traffic is increasing. I imagine at some point it will level off, and I won't feel so great about the project. On one hand, it's a "failure" because I've really gotten no buzz, have not seeked attention of the blogosphere, am not making the $15/mo I need to break even on it, etc, etc. On the other hand, it's something that is mine, forever, that I am proud of, and that has potential. And hell, it really works well. So, in terms of a "success," relative to the fact that this used to not exist and now it does, I've obtained it. In terms of "can I retire off of it," not so much.
PS: Here are some other URLs that might help you find out how to better track and engage your visitors (as well as showing off what my site does): http://www.moreofit.com/similar-to/mouseflow.com/Top_10_Site...