Since then, I've written something in that journal every day. For a few years I even included a daily photo.
There have been some hiccups along the way. When they switched to a new syncing system, I lost about 10 day of entries, which needed to be re-written. When I tried to export a PDF years ago, it choked under the weight of my photos and couldn't do it. This has taught me to always be cautious enough to make multiple types of backups (not just Time Machine or online backup) and PDF more often (now that it works).
It may sound like I'm not so impressed by the service, but there's no such thing as a perfect app. It's been two years since I've had any syncing issues, and it's been a solid otherwise. I always wanted an app for blogging just to myself, and Day One proved to be that app. Nothing else even comes close.
Recently they announced Day One Books, an easy way to publish your journals. The books seem well designed and if my journals weren't so private, Day One Books would be a much better alternative for creating my family photobooks than the typical options from Apple, Blurb or the local photo printer.
Shawn Blanc and the gang at The Sweet Setup did a deep dive into Day One in their ebook Day One In Depth. I haven't read it yet, but Shawn always does quality work. Check it out if you want quickly learn the ropes, instead of spending years in it like me.
I still recommend Day One after six years of use. It's the gold standard in personal publishing. And, until our photo programs wise up and incorporate mixed media (or at least text) to tell full stories and provide context, Day One is really the only game in town.