Today is Tu B'Shevat, the 15th day of the Jewish month of Shevat. It's one of those minor holidays that no one knows too much about. Then again, Tu B'Shevat enjoys wide familiarity because of its universal themes of nature and environmentalism.
The Talmud lists four "new years," the most famous of course, being Rosh Hashana. Each new year is significant for a different reason. Tu B'Shevat is the day that the trees are judged, i.e., it is determined how well they will grow, how fruitful they will be. Of course, this is really a judgement for man, because it is mankind that will benefit from a year of plenty.
Some people have the custom of having a Tu B'Shevat seder, at which there is a full spread of fruits, especially the seven fruits that the Land of Israel is praised by, the shivas haminim. These include pomegranates, dates, grapes and figs. Some people say a special prayer today to merit having a beautiful esrog, the citron fruit that is one of the Four Species. (Though that will not be relevant for several months, because today is when the judgement is made, it is a timely prayer.) A more modern way of marking the holiday is by planting trees in Israel, an idea fueled by Zionism.
One thing is sure: this is one Jewish holiday that can't upset nutritionists and health nuts. The emphasis is on fruit!