April 23 is St. George's Day, a holiday celebrated in Catalonia by the exchange of books and roses. Traditionally, the occasion was marked by the presentation of roses to women while in return women offered books to men. In time, the exchange of books became mutual. According to Wikipedia, the celebration of St. George's day accounts for half of the annual book sales in Catalonia.
April 23 also marks several literary anniversaries - on that black day in 1616, both William Shakespeare and Miguel de Cervantes died. Two hundred and eighty-three years later, Vladimir Nabokov was born on the same day. And three years after that, in 1902, Halldor Laxness, considered by many to be Iceland's greatest writer, was born.
Given the seemingly scripted significance of the day, UNESCO, in an effort to promote reading, writing and the protection of intellectual property, designated April 23 as World Book and Copyright Day. If for nothing else, the tradition provides an excuse to buy a book for a loved one - and, of course, to get one in return.