Hello, Greg Erwin here, new to this list, but old to the debate.
I would say that omni* will always involve some kind of contradiction. Though the real world is a place of random events with no overall purpose, human minds attempt to find patterns in it. This is an urge built-in (by natural selection). Christians assume that everything that happens serves the purposes of a creator and sustainer, and work backwards from the events to find the "purpose" every time. Seeing as they "find" a purpose every time, the obvious conclusion is that that the purposeful entity is omnipotent as 'everything' that happens is what he wants to happen.
However, things happen at cross-'purposes', things happen with no 'sense' to them. Unless your god is the indifferent Brahman, or the nature's god of the Deists, you cannot attribute purposes to what actually happens. Christians, unlike Hindus or Buddhists, will not admit a god that is repsonsible for both evil and good.
Well, enough for a a start.
-- To know that the Bible is the literature of a barbarous people, to know that it is uninspired, to be certain that the supernatural does not and cannot exist--all this is but the beginning of wisdom.--Robert G. Ingersoll / Greg Erwin, VP, Humanist Association of Canada