Orthodoxy is the pentecostal form of Christianity by excellence: we invoke the Holy Spirit with every opening prayer (“O Heavenly King”) and at every major liturgical acts (this is called the epiclesis). This is especially true of the Eucharist and of episcopal consecrations. The question then is not about the importance of the Holy Spirit in Christian life since in the words of St. Seraphim of Sarov: “the goal of Christian life is the acquisition of the Holy Spirit.” The concern seems to be on the specific “gift of tongues” or “glossolalia” which is very much emphasized among certain Chritian groups.
The short answer then, it that Orthodox theology has a clear understanding of what the gift of tongues means and what the parameters are. Regarding the “gift of tongues” (i.e. not the gift of actual foreign languages but the gift of unknown languages), this is not a gift that is actively sought, encouraged or present in Orthodox life for the reasons explains by St. Paul in his first letter to the Corinthians (1 Corinthians 14). There are a few Orthodox Christians who have shared their experience in regards to speaking in tongues, but again, this is rare, discreet, and not part of the normative experience of Orthodox parishes. Perhaps the only active promoter of a form of Pentecostal movement in Orthodox America is Fr. Eusebius Stephanou of the Greek Orthodox Archdiocese ( http://www.stsymeon.org/ ).
Orthodox Christians generally recognize that the gift of tongues (as distingued from “foreign languages”) existed in the early Churches and could continue to be manifested as God wills. At the same time, extreme caution is called for when it comes to spiritual gifts as the risk of demonic delusion is quite real. In all such cases, consultation with the bishop and an experienced spiritual father is advisable.