I write diary everyday. My parents helped me establish this good habit, and I have been benefiting from it for twelve years. This is a part of my life, and I have found it especially important when things are happening at such a rapid rate these days.
As soon as we wake up in the morning, there are all kinds of tasks that we have to deal with. We spend time on school, extracurricular, social life, money and so on, and we give so little attention to our soul and mind and real learning experience.
I need at least twenty minutes at the end of everyday to calm down and think about my day. What have I done? What have I learned? What is wrong and what is cool? How can I do it better tomorrow?
I found that when I start to write things down, my understanding will go into a deeper level. If I just experience without thinking and writing, I am wasting this precious chance of real learning.
What's more, writing diary also helps me to not to forget my Chinese =)
Blog is a very different thing. Blog is more like a show, a marketing strategy, a good way to publicize yourself and make your voice heard. Blog is too connected with the rest of the world. In comparison, diary is personal and intimate. So I can be very honest, though it can be painful sometimes =)