You can definitely use as a journal. Keeping a journal and personal history is one of the site's strengths. Here are some things to consider with journals on

Your journal will be created automatically as you use the site.
Most people who use find that journal writing happens as a natural side effect from normal site usage. As you post your own epistles about your life and your experiences, your journal will create itself. The biggest differences between the journal you use at home and are:
1) Your home journal probably isn't read by anyone until after you die.
2) Your home journal probably isn't kept in a facility secured with biometric scanners.
3) Your home journal probably isn't backed up to three unique locations each night.

Alternatively, you can keep your journal to yourself.
If you prefer to keep your journal entries private, but you like the online capabilities (make journal entries from anywhere, keep your entries secure, make your entries available online to others at some point in the future, etc.), you can create a group where you are the only member. Nobody can see your journal entries but you. You have your own place on the Web to keep your journal and your pictures. It belongs to you, and only you, until you decide to share it.

The ability to keep a journal while corresponding naturally with others is powerful. Let's be honest - it may be the only way that most of us will ever keep a journal. Keep up with your favorite people and leave a legacy at the same time by keeping your journal on