Oh my goodness, journaling!! This is near and dear to my heart!
I journaled big time in junior high and high school. I was never a nightly journaler. I would go in spurts and sometimes months would go by without an entry, but I always came back to it. I hated the term "diary" so I called mine my "MOLS" (My Own Life Story). LOL! Ah, memories. Mostly I wrote about boys. I wrote about whatever I had done that day. And if I didn't want anyone ever finding out what I had written, I wrote it in very bad Spanish!
I just picked up journaling again, actually, because I found myself obsessing about one particular life issue. These days I type far faster than I write so I started journaling by emailing myself. Gmail keeps a running log of emails contained in one long email so it works great. It allows me to get the obsession out of my head and gives me something to look back on. I write mostly about that obsession now, but also about cute things my kids have said or done, trips we've taken, things that have annoyed me, etc. It's very therapeutic!
I wouldn't say it has ever been a habit. It's time I look forward to, but often I forget or just don't feel like it. It became weird when I got married, I think. That's why I stopped. Always I was very honest about what I was feeling and I no longer felt like I could be honest. Plus, I ended up in a bad relationship. Now I wish I had journaled and I wish I had done so honestly because I don't trust myself as to when exactly I noticed this was not a good marriage. But I was also very sensitive to family reading whatever I wrote when I passed or if they happened to find it. My boys certainly don't need to know what or how I felt about their father. I still always have that in the back of my mind as I write. It's possible someone will someday find these half crazed thoughts of mine.