Having duplicate title tags is not the best thing. You should always strive to have unique title tags. If you can't have unique title tags then make sure the content is unique. As long as the content on the page is different you will be fine.
If you have duplicate content, for example let us say you have a product page and a print friendly page that has the same content. Google will not penalize your site. They will simply filter out one set of the duplicate pages.
If you want to control which set of duplicate pages is filtered out then you can use robots.txt.