I am personally unaware of any exact reference in a modern synodal ruling on this issue (though I do believe there to be one out there, at least as it relates to such things as last rights; and while there are several synods from several hundred years ago that have ruled on this issue, those rulings do not reflect modern practice); however, I am familiar with what the Synod of Constantinople has ruled in regard to Anglican Orders. Validity was essentially accepted, with some reservations, basically the decision said that all Anglican Sacraments are valid and if the Church of England were to enter into Communion with the Orthodox their Priesthood would be regarded as valid and no reordinations would be necessary; however, if an individual Anglican Priest were to convert to Orthodoxy while the Anglican Communion remained out of Communion with the Orthodox, then he would have to be reordained to function as a Priest. This decision seemed to use the reasoning that yes the Anglican Priesthood was valid, but that one is ordained within a specific tradition (technically to a specific parish even) and is only valid within the context of the Church in which the person in question was ordained. The customs and traditions of the Anglican Church are western, and thus foreign to the Orthodox, making their ordinations foreign to the Orthodox, who are inherently eastern. Now if the Anglicans were to have entered into communion with the Orthodox, then there would be a genuine and ancient expression of this western tradition within the Orthodox Church, making these customs no longer as foreign to us as they were (and are now); and, thus, making their priesthood acceptable within the context of the Orthodox Church.
Concerning specifically the Reception of Catholic Priests in particular, our response seems to be related but more tolerant (today, in any case). Most cases of which I am aware are cases in which the Priest (or deakon) was accepted as a Priest (or deakon), though I have also heard of cases where there was a reordination, our response on this issue has been far from consistant (a byzantine priest, however, is probably more likely to be received without reordination than a latin priest; though I know of cases where latin priests were received without reordination). However, it should also be noted that often our posistion is dependent not only on pure theological arguments or reasoning but on the practical element of inter-church relations. There is not much 'bad blood' between the Orthodox and the Anglicans, but there have been far more political problems between the Orthodox and the Latins (and the Eastern Catholics), which will often influence our responses.