A common misconception within the online community is that there are “penalties” for having duplicate content on your website. Many webmasters tend to get very antsy if they think the folks at Google et al are going to put them in “search engine jail” for having duplicates of this and duplicates of that on their website. In actuality, omission or de-ranking is reserved for only the most blatant offenders.
If your intention is to deliberately steal content from another website or spam your page’s content with keywords with the goal of ranking higher, then you should probably fear Google’s wrath. However, if some pages simply look very similar or are just duplicated because of a stubborn CMS, the worst that will happen is that one of these pages will simply be filtered out and demoted to the supplemental index. The best way around this is to either employ the proper redirects (a topic I discussed in my last blog post) or to make all pages on the site as distinct as possible.
Barring the iron fist of the search engines, it is still good practice to avoid duplicate content for the sake of your users. The more unique content on a website, the wider the reach you will have in the search engines and the better experience you will provide for your users.