I don't know what the future holds for Day One now that it has been acquired by Automattic but I know from my own experience that linking journalling to blogging, first on WordPress and now here with (b)log-In, that they are a natural fit — two sides of the same coin, a public and private side.
I had always struggled to keep journalling on paper. I looked at Day One but it didn't really fit my needs. It wasn't until I placed a journal within the same space as the blog, with the same updating mechanism, that it clicked for me. I've now reached a streak of 183 days — past the half a year mark, an achievement and milestone to be proud of.
Future integrations of Day One with WordPress and Tumblr make sense — a lot of sense and I think good things could come from it on both sides, the public and private.