For instance, Dallas Morning News keeps launching these auto-expanding ads and semi-interstitial ads that obscure or abruptly push down page content. Those irritate the heck out of me, and I doubt I'm alone.
I think tedster's advice can be applied to any landing page, not just the home page. After all, if you arrive via a search engine, you want to know where you are and what you can do there. I don't file these stats in my head, but there is some brief period, like 2 seconds, when you have to get the visitor's attention, else they leave.