Incumbent....Anyone Got an incumbent

Assuming Dick Chaney doesn't change his mind, the 2008 election will be relatively unsual in one regard. There will be no incumbent running on either side. For the purposes of this discussion, an incumbent includes the VP of a president who has been termed out.

Last time this happened? 1952 Eisenhower v. Stevenson. Time before that? 1928 Hoover v. Smith. Twice in 80 years or 20 elections, or 10% of the time.

That's about all the research I feel like doing right now. If anyone wants to find previous examples and post them, I'd love to see it.