Where There's A Will
In a recent article, George Will suggests the time for Obama is now. It's still a bit early to think about 2008, but in general, Will is right--Obama may not seem so exciting once we get used to him.
In his list of arguments for Obama, though, one is just filler: "...the odds favor the Democratic nominee in 2008 because for 50 years it has been rare for a presidential nominee to extend his party's hold on the presidency beyond eight years."
This is rather silly. There's simply not enough data to justify any particular trend--each Presidential election is pretty much a law unto itself.
The cutoff date itself is arbitrary--if Will had made it 100 years we'd see it's pretty common for a President to hand the torch to a member of his own party. In the other direction, politics has changed so much that I'm not sure if you can get many clues from things that happened before Reagan.
And let's look at those stats. We'll ignore Truman taking it after four FDR terms, since that's more than 50 years ago.
Nixon had a shot and lost narrowly. Humphrey had a shot and lost narrowly. Ford had a shot (even after Watergate destroyed the Republicans) and lost narrowly. Bush won after Reagan. Gore had a shot and lost narrowly, though he received more votes. And note these were all Veeps running, which won't happen in 2008.
Four out of five close cases going your way proves nothing.