Check out this article on John McCain's staggering campaign effort, from the NYT. This is a pointed validation of the danger of getting into the campaign too early. Just think about where McCain would be today if people were begging him to get in the race because they were unhappy with the rest of the field. Instead, the faithful are dying to have a Fred Thompson or a Newt get in to spice things up.
Perhaps this bodes well for future races as candidates realize the downsides of a two-year campaign.