Your high value landing pages: In his talk on the Web Analytics panel at SES, Avinash Kaushik recounted his experience searching for a new faucet. The top paid ad took him to a page focused on sinks rather than faucets; he was immediately turned off and bounced from the site.
What's the lesson here? Landing pages are key pages to optimize because they are your visitors' first (and often last) impression of your website. If a visitor lands on a page that doesn't provide the information she's looking for, she'll probably leave without clicking any further. For high-traffic landing pages, this can add up to a lot of lost visitors.