I have tried many times to make journaling a regular habit, but I never seem to maintain the habit for very long. Instead, I have just created a folder on my computer and when a particular mood strikes me or there is a memorable event in my life, I type up my thoughts. Since I can type much faster than I can write, I have found this to be a more effective means of keeping my thoughts in order.
It's wonderful to be able to go back and see how I felt at a given point in time. I wish I had the discipline to make journal writing a dedicated part of my day everyday.