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The only way i recovered these Serp's was sending a plee to yahoo, to their due they replied in a very short time with "expect to regain your rankings very soon" that was about 7 months ago.
To my knowledge i wasn't breaking any guidelines and there wasn't any information in the letter i received that mentioned that i had. I didn't change the site design due to Google loving it, so i don't think it was any thing i did.
But with no cache link next to your pages it definitely affects your rankings so similar to G's supplemental index I'd say yes.
Vimes.