Opinions online about forcing links on a website in a new tab seem to agree with what I've always resonated with; Leave the choice up to the user for internal links and force a new tab for external links (to reduce the amount of recorded bounces in analytics). This article has an interesting exception to this rule.
Of course, there are exceptions: in some situations it is right to open links in new windows and wrong to open links in the same windows. Jakob Nielsen (http://www.nngroup.com/articles/open-new-windows-for-pdfs/) suggests to use new windows in case the linked document is not a .html-document. In this case he recommends to use a pop-up-windows without browser control toolbar. In such case it is reasonable to let the user know upfront how the links will be opened.