Some notes on devotion to the Blessed Virgin Mary:
"Devotion to Our Blessed Lady in its ultimate analysis must be regarded as a practical application of the doctrine of the Communion of Saints." ("Devotion to the Blessed Virgin Mary", http://www.newadvent.org/cathen/15459a.htm)
"In Catholic theology there is a clear distinction drawn between the worship of latria (adoration, which may be offered only to God), and veneration and praise, or dulia. Catholicism has traditionally accorded to the Virgin Mary the veneration of hyperdulia, which rests in part upon the angelic salutation, "Hail, full of grace" (Lk 1:28), a phrase with momentous theological impact. Over the centuries, according to the Catholics, the nature of Mary within theology became clearer. By 403 we find Epiphanius refuting a sect called the Collyridians who adored Mary, telling them: "Mary should be honoured, but the Father and the Son and the Holy Ghost should be adored. Nobody should adore Mary" (in Ott, Bk III, Pt 3 Ch. 3, §8). Thus we find, from the third century Church, veneration of Mary. Later, the belief that Mary intercedes for us with her Divine Son, and a clear distinction between latria and dulia together with a rejection of the notion of giving latria to Mary. The saints, for their part, receive dulia. This distinction between latria, hyperdulia, and dulia, is key to understanding Catholic Tradition (the Orthodox do not distinguish hyperdulia from dulia)."
("Blessed Virgin Mary", http://en.wikipedia.org/wiki/Blessed_Virgin_Mary)