+1 here. I forget to log with Day One pretty often (even with their Mac notifications, which give you a text field to begin writing on), but I'm also not convinced that I was as much information as something like Slogger[1] gives me. Especially with things like the new M7 sensor in the 5S, there's huge potential for passive journaling where a great deal of information can be gathered locally without ever typing a word.
[1]: https://github.com/ttscoff/slogger