There are two things that Day One currently has going for it that MacJournal needs:
1. First, syncing through DropBox is dead easy, and, more importantly that means syncing **all** your devices, including iOS devices.
2. Day One offers a minimalist user interface for writing that doesn’t require one to go into full screen mode.
I know full screen is all the rage, but sometimes I want nothing more than a neatly-styled text box to type into that will then expand into a fuller UI if I want it. Scrivener almost gets this right except it doesn’t know how to adjust its width accordingly — this may be a function of Mac OS options than the app itself. I really like apps that grow and shrink their size modally, e.g. iTunes.
**UPDATE** (July 2012): I have returned to being a loyal user of MacJournal, which will shortly be beta testing syncing options, including through DropBox. My return is precipitated on a few things:
1. The developer of MacJournal is amazingly friendly and helpful and has been for years. I contacted the developer of Day One once, and I thought very respectfully, and his response was, well, to use an old-fashioned word, *churlish*. (It’s more polite than the first word that came to mind.)
2. MacJournal already offers almost all the functionality I want: tags, the ability to post something from the app to a variety of blogging platforms, the ability to include graphics in posts. It’s not perfect in this regard, but it’s got a lot packed in it.
3. I still prefer the UIs of the two Day One apps: they really are lovely, and I hope MacJournal’s developer has the chance to try some things out. It may be that his user base largely prefers things as they are — and since I am only one voice in a larger market, I have to respect that.