quesera - 8:49 pm on Feb 11, 2011 (gmt 0)
If you fairly and legally use another entity's (EXAMPLE.com) content, according to their license, that's fine and expected.
If you create a site under a domain that appears to be intentionally confusing (EXAMPLEonline.com) or implicative of involvement or endorsement of that other entity (EXAMPLEnews.com), and then duplicate their content, you're likely to irritate them. In many jurisdictions, they have legal recourse. If EXAMPLE is trademarked, even more so.
There are special allowances for parody and criticism sites (EXAMPLEsucks.com), but those allowances are generally voided if there is no parody or critique of the content.
The most popular online encyclopedia site and the most popular online classifieds site deal with this sort of thing often. Their responses vary.