Keeping a diary in Japanese is a great study technique. A weblog ("blog") is a web site which functions as an online diary. Blogging in Japanese achieves similar aims to a paper diary except that it is your typing which will improve, rather than your orthography, and in lieu of privacy your daily adventures will be accessible to millions of people. Assuming you are sensible enough not to post the most intimate revelations of your fetish for barnyard animals a blog has certain advantages over paper.
1. No stress over remembering how to write kanji - just enter the reading and the computer does the rest.
2. Learn valuable computer skills.
3. No more worrying about carrying a journal around - if you use a web based blogging client you can update from any internet-enabled computer.
5. You could become famous on the net
6. Complete strangers will write helpful comments on how you can improve your Japanese writing.
For your reading pleasure I have set up a basic journal blog in Japanese called Nihongoblog. I daresay there are mistakes in the Japanese, but someone will comment on them and then everyone gets wiser.
If you get an application which allows moblogging - a mobile phone, PDA, Blackberry or Bluetooth enabled digital camera - you don't even need a computer. (Well theoretically you could read blogs on your mobile devices too)
It only takes about 10 minutes to set up a basic blog. Here are some blogging clients - all are free, though some for a limited time. All allow posting in Japanese although Greymatter has had some issue with comments.