The Presanctified Liturgy "of St. Gregory the Dialogist"?
Huw Raphael has posted some interesting comments about Fr. Hopko's papal reunion proposal. In a separate entry, he asks whether Pope St. Gregory the Great actually composed the (very) Byzantine Presanctified Liturgy of St. Gregory the Dialogist.
A few years ago, I noted this ascription was dubious.
The OCA website on the topic has jettisoned the popular Eastern assumption:
The Liturgy of the Presanctified Gifts is traditionally considered to be the work of the sixth-century pope, Saint Gregory of Rome. The present service, however, is obviously the inspired liturgical creation of Christian Byzantium. 
Essentially, Uspensky argues that it's based on a corrupted text of a postscript to a life of Saint Gregory written by Saint Photius. The original postscript read: "It is said that [Gregory] laid down the rule that the full liturgy be celebrated in the Roman Church on fasting days, a rule observed by them to this day."
Several centuries – and several battles with Latins – later, this text, as it had come to appear in the Greek Synaxarion for March 12, read: "It is said that [Gregory] is the one who laid down the rule that in the Roman Church on the fasting days of Great Lent the Liturgy of the Presanctified is to be celebrated, and it is celebrated to this day."
The idea is that Gregory, as a Western Saint venerated by both Latins and Greeks, might be a good guy to enlist in support of the Byzantine practice, in order to convince the Latins how wrong they are.
That is a somewhat mixed bag. The liturgy's seemingly clear amalgamation of "solemn lenten Vespers with the administration of Holy Communion added to it" and its Byzantine mannerisms -- full prostrations in the Slavic practice -- do not seem terribly "Gregorian." The clincher to me is that, despite the fact that Pope St. Gregory the Great stayed at the court in Constantinople, he made it a point to never learn Greek  -- which would have made his career as a Byzantine liturgical innovator difficult, to say the least.