There's really nothing to improve with the Day One app. It's perfect.
Day One is a journaling application for iOS and the Mac. You can use it as a personal journal, a work journal, a commonplace for random thoughts, a record of your tweets (if you compose the tweet in Day One first), or as a scrapbook of memories (since it can incorporate photos). It is, as Day One calls it, your personal history.
It delights, with its movements, sounds, and integration. It slides in and welcomes you with a place to enter whatever you may want. I particularly like it for capturing those quick moments: a great meal, something the kids are saying or doing, an interesting place or image. Take a photo, enter a few lines of text, and your're done: a quick, perfect record of a moment, place, or event. Since it is a smartphone, it has recorded the time, location, and even weather conditions; all of this meta-data is included. If you add a photo after it was taken, it's clever enough to notice the discrepancy and ask if you want to back-date the journal entry. Genius. There is a companion Mac app that syncs and provides another way to quickly enter text.
What I really enjoy is making my own private social network with it: instead of publicly sharing a record of my life with Twitter/foursquare/Instagram/facebook, I'm making a private record of my life and important moments. If you record these things in Day One first, and then send them from Day One to these networks, then you have a backup of these thoughts and moments outside of facebook and Twitter. What happens when a Twitter server deletes some of your tweets, your blog is hacked, or foursquare gets bought up and discontinued? These records of your life are gone. But Day One provides you a local and accessible copy, in XML, so it should be relatively future-proof.
Thank you, Bloom Built, for a perfect application.