(Disclaimer: this app is not free)
On their blog (inexplicably a Tumblr?) they talk about developers extending Reporter on their own? But I'm nowhere near that kind of tech-alpha level.
Personally I've liked it a lot, it has huge potential, but it's definitely closer to a prototype than a full-fledged product IMO.
Like the only thing you can track over time seems to be numbers, but I'd like to see people or "tokens" (tags) tracked over time as well. Also with numbers, there's no counting built into the questions - so if you're tracking the number of times you've had water today, for instance, you have to keep track yourself your cumulative total when you submit a report.
I really hope the people behind the app keep working on it and improving it and don't sell it out. So many of my favorite apps have died that way :-\ (Pulp R.I.P.). High hopes!