I have kept a regular journal since I was about 8 years old (I'm 27 next month), and I have never regretted doing so. I've gone through probably 25+ bound journals, usually bought from the journal section at Barnes and Noble... mine MUST be unlined, because I hate feeling that restriction on my writing!
And sure, occasionally a friend or parent would stumble across my journal, and I'd freak out... but usually it didn't end up being a big deal, and when I was a teenager, it was probably better if people knew what was going through my head anyway. As years pass, I care less if anyone reads my older journals, because the issues I wrote about have become irrelevant over time and are instead just a record of who I was in that season of my life.
The peak of my journaling was in college, when I would write for 30-60 mins every day, on average. Sometimes longer. I filled up book after book after book... I couldn't live without writing every day. Then, after college, I slowed down a bit since I started teaching high school and that consumed most of my waking hours. I went to Iceland and started journaling furiously again, since I had more time and space to think there... it was very freeing to journal in that beautiful, quiet place. I figured out a lot of things about myself by journaling in Iceland. It was a key part of my development.
Eventually I made it to grad school and kept writing, though once I started dating ktspktsp, my journaling tapered off significantly. It was important for me to start it up again, since I was not setting aside much time for myself in the relationship... so after a year and a half, I think, I got back into it. I've been trying to keep it up regularly since then.
Well, I don't think that was what you were looking for, but hopefully it was semi-interesting.
Good luck, and there really isn't much harm in journaling. Find a good place to hide it, and you're set!
And genuinegirly: I prefer those PaperMate black pens, too... simple is best for me.