I think the 3 year thing that Goonarmy speaks of is pretty accurate, and seems set to become the norm. I hope not. There is evidence though.
Sunderland came up, embarassed themselves completely (lowest total ever?) went down, and now find themselves back in the Premier League, doing well(-ish) and should stay up. The same could be possible for Derby, who as GA says could go down, benefit from the money they earned in the league and the big investor they snapped up whilst part of it, in order to come back up. It would be a sorry state if it all went that way, but I guess it still turns out that a Championship side, who did well in a given a year, and deserved their Premier League run, achieved it...albeit 2 or 3 years after their first stint in the league.
The Premier League goes from strength to strength and its good to see the competitiveness of the Championship never dies. As long as it never ends up the same 3 teams going up and down each year, then we dont have a massive problem.