The feed is confusing. It looks too much like Instagram, so it contradicts the idea that this is an app for sharing actions rather than just pictures.
The top activities are plankaday (what's that?), write, sleep, run, and meeting(!). None of those are too interesting. So, I'm not getting a feel for what is this app really good for? Why don't you show more activities rather than just the top 5?
The actions are not very specific, that's probably why they don't seem interesting to me.
I bet you get this a lot, but really, if I'm using Runkeeper or another similar app for my exercise tracking and sharing, why should I use didthis? One possible answer is to push actions to those apps (I haven't tried it if you already do).
The quality of the experience will probably go up dramatically if you choose to focus on a single type of action or community. Everyone keeps repeating this and from recent personal experience, it does seem true.
Social causes seem like a good one to go for, but the problem there is frequency of use. I doubt many people volunteer or donate more than a few days a year. This is the kind of app that people need to use at least once a day or it will die.
I like your deed of the day idea. It might be worth zooming in on. What if your app was totally based around that? Daily deeds?
Finally, you better not steal my contacts! If you do, start working on that apology letter right away.