WordPress 2.0 has a preview feature that can cause Adsense problems:
“… because the post hasn’t been published yet, when Google’s bot tries to crawl the page a few seconds later, it will receive a 404 error.”
Google prevents placing ads on 404 pages, as wel as pages hidden behind a login, so you might get banned from Adsense. Or if not, get poorly targeted ads on the posting when published. Another annoying feature for stats junkies, are the invalid page hits.