In terms of this being the start of Australia's decline (I presume we're talking in the context of ODIs here), it's just all a bit too sudden for me to see it that way. We've just lost six out our last seven games against teams we were beating comfortably only days earlier. I think something more meaningful is demonstrated over a slightly longer period, a team doesn't just break instantly like that. We've had a few injuries, the other teams (in England's case finally at the fag-end of the tour) found some spirit, and we've had a bit of a trough (not all of it being down to our bowlers, either). So for all our soul-searching, I don't think there's any radical answers, and I don't think it necessarily means we have to dramatically alter the side, either (outside of any changes necessitated by injury).
I do think we've had a problem defending big totals in ODIs for some time now, and that's something we really have to work on. Aside from that though I wouldn't be too panicky for the moment, unless we're astonishingly bad in the WC. Test cricket is a game that in general reinforces any disparity between the two sides, but the nature of one day cricket is different, and there simply isn't the same gap between the top and the rest, although it must be said that the Australians have done a great job of turning dodgy situations (which they actually encounter fairly often) into wins. Losing Symonds and going without Gilly and Ponting (as well as McGrath looking a touch fatigued and Lee getting injured) has had an obvious cost, where I think maybe some people assumed it wouldn't show.
On our last tour of the Caribbean, we won the first four ODIs in a best of seven matchup, and then lost the next three. OK, somebody will point out that they were dead games, but after the fifth was lost, I have no doubt that the Aussies wanted to reassert their dominance (particularly in light of losing the final test also, in a big fourth innings run-chase). This would have only doubled after the West Indians won the next ODI, before winning a third in a row to close out the tour. It felt at the time that if we'd played another, they'd have won that too. Sometimes things go wrong and the other team either digs deep or realises they have nothing to lose. A lot's happened since that tour though.
Having said all this, perhaps we'll flop from here. But losing in such succession after looking as strong as ever (to the point where people were bemoaning the lack of competition) just implies to me an aberration rather than something more portentious. You don't lose all that in a matter of a week and a half or two weeks.