Manton Reece, maker of Tweet Marker, Watermark and Tweet Library Wrote a response to Mat Honan's article from last week. In his response he wrote about the app he is working on:
"It uses the App.net API, but not the timeline. It takes pictures, but isn’t really a photo app. It integrates with Ohai, but isn’t another location check-in app. It renders beautiful maps throughout, but isn’t about navigation. Some of the features I’m most proud of in the app wouldn’t be the same without App.net. "
I liked his article and his app idea and I suggest you check it out.