To make this concrete, here's an example from Clarky Shirky's "Cognitive Surplus."
In the body of the text (left) the text "notes in his book The Success of Open Source" (which I've highlighted in blue) is a hyper-link. Click on it, and we see the source of the citation (right), together with the text that formed the hyper-link. This context helps remind you why you wanted to follow up the citation, and also provides the way back to the text: click on the context snippet and you're taken back to the original page.
Providing context for a citation is a nice feature, and there are various ways to do this. For example, the Elsevier Life Sciences Challenge entry by Wan et al. ("Supporting browsing-specific information needs: Introducing the Citation-Sensitive In-Browser Summariser", doi:10.1016/j.websem.2010.03.002, see also an earlier version on CiteSeer) takes a different approach. Rather than provide local context for a citation in an article (a la iBooks), Wan et al. provide context-sensitive summaries of the reference cited to help the the reader judge whether it's worth her time to fetch the reference and read it.
Both of these approaches suggest that we could be a lot more creative about how we display and interact with citations when viewing an article.