Perhaps, I have different experience, I bought dropped domains, .biz and .co and they are well-indexed. One of the .co dropped domain stays firmly on page 4 google US, it posts dominate google monthly and yearly for its keyword. It also on the first page of google blog search. I have to admit content is king no matter what. Thanks to google panda and penguin. My point is, how about considering buying dropped domains that is keyword oriented, put good content on it and you will see how good google really are. Once again, thanks to panda and penguin. Thank you again!
Drop domain is domain that do not continue to renew after expired and the domain name is pending delete and soon able to register by others.
Domains bought after their registration ends are called as dropped domains. So in easy words, expired domains are called as dropped domains.
That's a good question. If I buy one of them I check this article, it seems to cover the subject really well. http://enormoney.com/seo/buying-high-pr-expired-domains/