Broadly speaking, referring to a work is not something that is protected by copyright law. Several courts have ruled that some kinds of "deep linking" to a part of someone's web site constitutes copyright infringement. Other courts have ruled that some forms of linking are not protected by copyright law. The rules are not uniformly settled, either within the USA or internationally.
As one example, a lawsuit between two Scottish newspapers. I'm not sure what the court ruled on copyright-wise, but the final judgement basically said that by deep-linking and bypassing banners and advertisements, the offending newspaper was passing off the plaintiff's work as its own and defrauding it of its rights to advertising income and to being known as the owner of the work in question. You'll have to search for more details, this is just my recollection.
Cheers, Wol -- Anthony W. Youngman - wol at thewolery dot demon dot co dot uk HEX wondered how much he should tell the Wizards. He felt it would not be a good idea to burden them with too much input. Hex always thought of his reports as Lies-to-People. The Science of Discworld : (c) Terry Pratchett 1999