I hijacked this article from Benjamin Andersen's blog: http://occidentalis.blogspot.com/
Well worth the read...
A fascinating article on the problem of the filioque by Father Theodore Stylianopoulos, from The Greek Orthodox Theological Review (1986). Here are Father Theodore's conclusions:
"Two key factors are crucial to the ecumenical settlement of the filioque question. The first is the recognition that the theological use of the filioque in the West against Arian subordinationism is fully valid according to the theological criteria of the Eastern tradition. In the West the filioque has been used to stress: (1) the consubstantial unity of the Trinity, (2) the divine status of the Son, and (3) the intimacy between the Son and the Spirit. All these points are also integral elements of Eastern trinitarian theology anchored on the Cappadocian teaching of περιχώρησις ("mutual indwelling") of the persons of the Trinity, a teaching reflected by the Nicene Creed which professes an equal worship and glorification of the Holy Trinity. Thus a fundamental and wide agreement exists between Eastern and Western trinitarian doctrine affirming the complete reciprocity and mutuality of the Son and the Spirit in their eternal relations (immanent Trinity) as well as their manifested action in creation, Church and society (economic Trinity). Christ is both the bearer and the sender of the Spirit. The Spirit of God is in every way also the Spirit of the Son.
"The second key factor in the resolution of the filioque question is the recognition that biblical and patristic theology commonlly affirm the teaching of the "monarchy" of the Father, i.e., that the Father is "the sole principle (ἀρχή), source (πηγή), and cause (αἰτία) of divinity" (Klingenthal Memorandum). This teaching is of decisive importance to Eastern trinitarian theology and a teaching which the filioque clause in the West, according to contemporary Western interpretations, has never intended to deny. However, the Augustinian interpretation of the filioque, i.e., that the Father and the Son are the common cause of the eternal being of the Spirit, unintentionally compromises the "monarchy" of the Father according to Cappadocian trinitarian theology presupposed and reflected by the Nicene Creed in which the verb "proceeds" (ἐκπορευόμενον) refers to the eternal origin of the Spirit from the Father. Eastern trinitarian thought as expressed by Gregory of Nyssa, Gregory the Cypriot and Gregory Palamas conceives of the Son as mediating, but not causing, the Spirit's procession from the Father. On this nuanced difference in doctrinal interpretation hangs the whole weight of centuries of controversy between the Eastern and Western churches. The formula "who proceeds from the Father through the Son" is a sound theological resolution of this problem in the conciliatory spirit of Maximos the Confessor laying aside the above specific Augustinian interpretation as an erroneous theological opinion but at the same time affirming the active participation of the Son in the eternal procession of the Spirit from the Father.
"Finally, the filioque question does not signal a "great divide" between the Eastern and Western churches because these churches commonly confess the dogma of the Holy Trinity and share broad agreement regarding the work ("economy") of the Spirit according to Scripture, tradition, and liturgy. The filioque marks not a decisive difference in dogma but an important difference in the interpretation of dogma due to the differing Cappadocian and Augustinian approaches to the mystery of the Trinity. The theological implications of this difference are a more consistently biblical and personal understanding of the Trinity as concrete persons and careful avoidance of any modalistic tendencies confusing the uniqueness of each of the divine persons. The well-known critique that the filioque subordinates the Spirit to the Son and thereby "depersonalizes" the Spirit seems to express theological polemic rather than theological truth. As far as the practical implications of this difference is concerned, i.e., the often repeated charges that the filioque leads to authoritarianism, institutionalism, clericalism and other similar tendencies, one is hard pressed to demonstrate these historically and theologically because such tendencies, as well as their opposites, have existed in most churches with or without the filioque. More fruitful for further study are the specific implications of the Augustinian and Cappadocian approaches to the Trinity and theology in general, especially the implications for life, spirituality and practice. This kind of direction in ecumenical theology would be welcome because, next to and after a resolution of the specific filioque question, which is a highly nuanced question of trinitarian theology, such a direction would help focus attention on the wider role of the Spirit in the churches, society and creation today."