For example, I have a blog at wordpress.com then I bookmarked it to 100 bookmarking sites using different title and description used at wordpress.com. But all the 100 bookmarks are with the same title and description. Will Google consider it as duplicate content?
it's best if you use different description in each, you are right about that but a link is a link, with social bookmarking sites you are building for traffic. I recently wrote in my blog the benefits and misconceptions of socialbookmarking links, might want to check it out.