I just read through a great article (in Japanese) that gives advice to people about how to take great pictures of the cherry blossoms at night. There is a lot of basic advice for using the white balance and experimenting with your cameras automatic settings, but the site also features some nice photos of cherry blossoms at night.
Going to the same park in the afternoon for traditional “hanami” and then again at night for “yozakura” can be a lot of fun and give viewers a whole new experience at the same place… or if you have the time and enough energy to do it, why not go in the afternoon and stay until night?
Here is the article I mentioned above on a well-known digital camera blog.
Tricks for taking photos of sakura at night with a compact digital camera (in Japanese)