What is the SEO opinion of interstitial ads?

Does anyone have any facts or guidance on the SEO impact of using interstitial ads? They appear on a number of “big budget” sites like top-tier newspapers, magazines and video sites yet my guess is that Google and others would take a less favorable view of small sites using these ads. They are quite admittedly annoying, but can be profitable and beneficial in some situations.

Does anyone have any first-hand experience working with these ads and the results (good, bad or non-existent) from the various search engines?

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