Checking Wikipedia we found very interesting things about this celebration...
(Saint) Valentine's Day is a holiday celebrated on February 14 by many people throughout the world. In the West, it is the traditional day on which lovers express their love for each other by sending Valentine's cards, presenting flowers, or offering confectionery. The day was originally a pagan festival that was renamed after two Early Christian martyrs named Valentine. The day became associated with romantic love in the circle of Geoffrey Chaucer in the High Middle Ages, when the tradition of courtly love flourished.
The day is most closely associated with the mutual exchange of love notes in the form of "valentines." Modern Valentine symbols include the heart-shaped outline, doves, and the figure of the winged Cupid. Since the 19th century, handwritten notes have largely given way to mass-produced greeting cards. The sending of Valentines was a fashion in nineteenth-century Great Britain, and, in 1847, Esther Howland developed a successful business in her Worcester, Massachusetts home with hand-made Valentine cards based on British models.
Valentine's Day has regional traditions in the UK.
In Norfolk, a character called 'Jack' Valentine knocks on the rear door of houses leaving sweets and presents for children.
In Spain Valentine's Day is known as "San Valentín" and is celebrated the same way as in the U.K, although in Catalonia it is largely superseded by similar festivities of rose and/or book giving on La Diada de Sant Jordi (Saint George's Day).
In Portugal it's more commom refered to it as "Dia dos Namorados" (Boy/Girlfriend's Day).
In Denmark and Norway, Valentine's Day (14 Feb) is known as Valentinsdag. It is not celebrated to a large extent, but a lot people take time to eat a romantic dinner with their partner, to send a card to a secret love or give a red rose to their loved one.
In Sweden it is called Alla hjärtans dag ("All Hearts' Day")
In Finland Valentine's Day is called Ystävänpäivä which translates into "Friend's day". As the name indicates, this day is more about remembering all your friends, not only your loved ones.
In Estonia Valentine's Day is called Sõbrapäev, which has a similar meaning.
In Slovenia, a proverb says that "St Valentine brings the keys of roots," so on February 14, plants and flowers start to grow. Valentine's Day has been celebrated as the day when the first works in the vineyards and on the fields commence. It is also said that birds propose to each other or marry on that day. Nevertheless, it has only recently been celebrated as the day of love. The day of love is traditionally March 12, the Saint Gregory's day. Another proverb says "Valentin - prvi spomladin" ("Valentine — first saint of spring"), as in some places (especially White Carniola) Saint Valentine marks the beginning of spring.
Valentine's Day is called Sevgililer Günü in Turkey, which translates into "Sweethearts' Day".
According to Jewish tradition the 15th day of the month of Av - Tu B'Av (usually late August) is the festival of love. In ancient times girls would wear white dresses and dance in the vineyards, where the boys would be waiting for them (Mishna Taanith end of Chapter 4). In modern Israeli culture this is a popular day to pronounce love, propose marriage and give gifts like cards or flowers.
Central and South America
In Guatemala, Valentine's Day is known as "Día del Amor y la Amistad" (Day of Love and Friendship). Although it is similar to the United States' version in many ways, it is also common to see people do "acts of appreciation" for their friends.
In Brazil, the Dia dos Namorados (lit. "Day of the Enamored", or "Boyfriends'/Girlfriends' Day") is celebrated on June 12, when couples exchange gifts, chocolates, cards and flower bouquets.
Thanks to a concentrated marketing effort, Valentine's Day is celebrated in some Asian countries with Pakistan, Singaporeans, Chinese and South Koreans spending the most money on Valentine's gifts.
In Japan, in 1960, Morinaga, one of the biggest Japanese confectionery companies, originated the present custom that only women may give chocolates to men. In particular, office ladies will give chocolate to their co-workers. Unlike western countries, gifts such as candies, flowers, or dinner dates are uncommon. It has become an obligation for many women to give chocolates to all male co-workers. This is known as giri-choko (義理チョコ), from the words giri ("obligation") and choko, ("chocolate"), with unpopular co-workers receiving only "ultra-obligatory" chō-giri choko cheap chocolate. This contrasts with honmei-choko (本命チョコ); chocolate given to a loved one. Friends, especially girls, may exchange chocolate referred to as tomo-choko (友チョコ); from tomo meaning "friend".
In South Korea, women give chocolate to men on February 14, and men give non-chocolate candy to women on March 14. On April 14 (Black Day), those who did not receive anything on the 14th of Feb or March go to a Chinese restaurant to eat black noodles and "mourn" their single life. Koreans also celebrate Pepero Day on November 11, when young couples give each other Pepero cookies. The date '11/11' is intended to resemble the long shape of the cookie. The 14th of every month marks a love-related day in Korea, although most of them are obscure. From January to December: Candle Day, Valentine's Day, White Day, Black Day, Rose Day, Kiss Day, Silver Day, Green Day, Music Day, Wine Day, Movie Day, and Hug Day.
In China, the common situation is the man gives chocolate, flowers or both to the woman that he loves. In Chinese, Valentine's Day is called (simplified Chinese: 情人节; traditional Chinese: 情人節; pinyin: qīng rén jié).
In the Philippines, Valentine's Day is called "Araw ng mga Puso" or "Hearts Day". It is usually marked by a steep increase in the prices of flowers.
The Middle East
In Iranian culture, Sepandarmazgan is a day for love, which is on 29 Bahman in the Jalali solar calendar of Iran. The corresponding date in the Gregorian calendar is February 17. Valentine's day is currently celebrated in Iran despite some restrictions made by government; young Iranian boys and girls are seen on this day going out and buying gifts and celebrating.
In Saudi Arabia in 2008, religious police banned the sale of all Valentine's Day items, telling shop workers to remove any red items, as the day is considered an un-Islamic holiday. This ban created a black market of roses and wrapping paper.
Now, What are you plans to celebrate this very lovely Day?
Taken from: Wikipedia