If you worried about duplicated content may Duplicate Content, and Wrong SEO Plugins by Planet Ozh will help you.
This plugin will Keep your content safe from the duplicated issue, but about optimized search engines actually is not be a plugin’s job, it is your theme’s job, it must be coded and designed for it.
Top engine like Google expects that your blog is free from duplicated content. But how we do when the front page, category and tag pages, archives, search results, feeds, and a lot of places on your blog has a same entry, google will see it as a duplicated content. It’s expected. but If it weren’t there, it would be not be a blog..
While Ozh’s help blogger to minimize the amount of duplicated content on a blog using excerpts rather than full content, let’s not forget that the original intension of page rank is targeted towards those who scrape your content, or against splogs who use redundant content to fill up a blog, using spam links and such scam evils.
Here are a tips for reducing a penalty from duplicated contents:
1. Set multi-post views to excerpts, not full content, except on the front page and feeds if you wish.
2. Take care when you are copying another’s content to keep it within Copyright Law’s Fair Use restrictions to 10% of the content or 400 words. Write with your own words to make a differentiate between copied content and the originalls .
3. Dont use feed scraper or automatic feeds plugin that replaces your content with a full or excerpted content from others blog. If you use incoming feeds, feature only title and first 100 or less words of the your blog.
Thats enough,you can relax after its done. Remember, that duplicated content within a blog is expected. Duplicated content between blogs is not and will be penalized.