I've kept one for the last 6 years I believe, although I don't write in it as often anymore because I'm at a really good place in my life now. I think I started it partly as an outlet because I was an emotional, confused teenager, and partly because I'm a writer at heart and writing things down just fulfills me in a way. I've kept tabs on all the major (and not so major) things that have happened in my life and how it made me feel, including all my realizations and lessons learned. It's a neat thing to look back on to see how much I've grown as a person.
Though yes I do right about boys, journals are primarily for introspection. I write about an event or conflict that happened and then write about why someone may have said what they did or how I want to react in the future if the problem should arise again. By writing about the issue, I'm forced to really think through what happened and sometimes it helps me get through the trauma.
As for your second question, I for one am very introspective, though I am not introverted. I tell friends about what I'm going through and am not terribly shy or anything like that. I also don't think I'm more romantic than others simply because I keep a journal. I don't think it affects how you think of romance.
I have a diary from the 9th grade, with more than 60 pages of writing in it about everything! mostly to the category of romance and fantasies, what's goes on in the mind of a teenage girl who is lost and just needs to write it out, I was really confised last year but for some reason I've changed and grown to where I'm happy and don't need to write in a journal/ diary. It really a way to express your bottled feelings for people who are depressed at times. I started writing the first of my 9th grade year when my first love cheated on me. Let me tell you, I went all Adele on that year :p Only one person has read my WHOLE diary, my other friend said she couldn't read any more of it then she started to cry. It was written with passion, hurt and love, every single word. Also there are lyrics from a song. I always look back at it sometimes and cry.
A lot. Well I write a lot anyways. E.g. yesterday's page = song lyrics, random crap about the guy I like, a note to self not to eat the chocolate muffin in the kitchen, how much I want this pair of Sam Edelman boots, my view on a book I read... it goes on.
I write down a lot of the stuff that most people would be bored of if I bothered telling them (:
I call my writing (on my private site) my "diary/journal" I guess. I write about everything, & it goes in spurts...lately, the past year or so, it's mostly been about hurting & love. When I step back & I look at it from when I started it, I can totally sit & see all the places I've gone emotionally...like a story. Crazy.