The winter of 2006-2007 has been much warmer than usual and the Asahi Shimbun is reporting that this year could set a record for the earliest blooming of sakura in Japan. In an article about the sakura forecast for 2007, the Asahi Shimbun says:
Cherry blossoms, nature’s way of saying spring is here, are likely to burst into bloom nationwide four to five days earlier than usual, a private meteorological company predicts.
On a related note, sakurazensen.com (sakura zensen means cherry blossom forecast) has some interesting graphs. Even if you cannot read Japanese like me, you can kind of understand what is going on. Where the line for the year hits the pink line, that is expected bloom date.
Also be sure to check out this table for average temperates in Tokyo by year/month and their respective bloom dates.