Some philosophers hold that the power of a deity or sub-deity is directly proportional to the number of its adherents.
Thus, Jehovah and Jesus can claim to be the most powerful deities, with approximately two billion Christian followers. Allah, with 1.3 billion followers, and Brahma, Vishnu, Shiva, and the other members of the Hindu pantheon, with about 900 million faithful, fall second and third respectively. Those deities which have been lost from human consciousness have simply ceased to exist.
If this proposition can be accepted, then certain consequences follow. While the Norse and Greco-Roman gods remain with us in name, and may even be employed in epithet, no contemporary human is likely to tremble upon receiving Odin's curse, and a prayer to the Goddess Fortuna will leave one's pockets as empty of gold as they began. The old gods are more like favorite grandparents today. They amuse, they tell illustrative and amazing stories, and they pull coins from our ears, yet they have no ability to shape our destinies. We name our children after them, but Diana is no more likely to bring a stag home for dinner than to put an arrow through her lover's heart.
In many parts of the world, the gods and goddesses are as they have been from time immemorial; the rocks, the river, the night-stalking beast. And within their own realms they are no puny gods. Twilight, for we "modern" humans caught away from the plastic and steel of our own created world, is a time of wonderment and unease. The gods walk. And where there is belief, there is power. A believer cursed by a Voudoun shaman will die. Period.
It can, in fact, be argued that we create our own gods. Jehovah, the Hairy Thunderer, did not spring fully formed from some Cosmic Limo, bursting upon the world as a Divine Fait Accompli. In fact, Jehovah (or the much more benign "God" into which either he has been morphed or replaced by - the jury is still out) cannot hold sway over even a simple majority of the population of this planet. He is a stitching-together of bits and pieces of Ahura-Mazda, the Dual God of Persia, and the Egyptian gods Horus and Set-Anup, who represented the duality of goodness and evil, light and dark. He is a patchwork of Zoroastrian and Indo-European gods.
Now Satan is a deity of the times. Talmudic scripture contains virtually no reference to Satan, and a specific deity or power of Satan's nature plays no role in traditional Judaism. In the Old Testament, Satan has little independent power, and takes on the role of an accuser (Samuel), an antagonist (Numbers), and a prosecuting attorney against mankind (Job). Even Jesus' involvement with Satan was no more heated than an attempt by Satan to put Christ off his self-imposed exile in the desert. However, with the rise of Islam, and the Old Religions of the Celts not yet cold and dead, Satan's time for a promotion had come. In fact, his greatest influence as a deity was felt during the Middle Ages, during which time even the Holy Roman Church was caught in a madness which resulted in acts of unspeakable evil being committed upon tens of thousands of people. As we move into the new millenium, though, we see the enormous power Satan held until the Renaissance diminishing. Where is that power today, beyond what can be seen (and felt) of the rag-tag swirlings within the Christian Fundamentalist movement? We know where the Great Satan is today - he springs from our own fingertips.
While there may be some vestigal power in the old names--while I would no be concerned about safes falling on my head as a recipient of Odin's curse, I might take extra precautions crossing the street--a request by a disgruntled Slovak shopowner that "Perun smite me" would only leave me wondering whotheheck he was talking about. The Thunder God, a supreme deity of of the Indo-Europeans prior to the separation of the Aryan "race", is who. But a supreme deity whose modern presence is that of a faint draft in a closed room.
Apsu and Tiamat exist today only in impressed markings on clay tablets. They who held up the sky of the Babylonians, who caused the wind to blow and the rain to fall, have left, and it is only their bones which lie still now in the back shelves of Turkish curio shops, or which were blown to dust by the armaments that struck Iraqui museums. Not even epithets remain.
Further reading:
Religions by Adherents => www.adherents.com/Religions_By_Adherents.html
The Old Gods => http://www.sacred-texts.com/neu/srp/srp05.htm
Babylonian Gods and Goddesses => http://ancienthistory.about.com/cs/egypt/a/babygodsindex.htm
The Devil is Divine => http://www.truthbeknown.com/devil.htm
The Origins of Good and Evil => http://www.truthbeknown.com/devil.htm
Satan => http://skepdic.com/satan.html