For all of you interested, there is a new Japanese IME that harness the web 2.0 social power, and is properly called the Social IME.

Social IMEは、ユーザー参加型の新しい日本語入力ソフトウェアです。 みんなで単語や正しい変換結果を覚えさせることで、どんどん賢くなっていきます。

"Social IME is a new Japanese input software that takes form thanks to user participation. It gets smarter as everybody provides it with vocabulary and correct conversions."

When you write using a Japanese IME, the more you use it, the "smarter" it gets. For example, sometimes you don't get the result you expected when you write a word for the first time, but when you write it again the system will remember the kanji you used the last time, so it will show the same combination as first candidate. The main idea behind Social IME is that the dictionary is shared by lots of people, so it gets smarter at a faster rate and produces better results, improving writing accuracy and speed.

The only downside to Social IME is that you need to be online to use it, and if your connexion is pretty slow it could affect the time it takes to write in Japanese. If you have a good connexion, though, write a lot in Japanese and feel the IME you're using is slowing you down, it could be an interesting option.