Now here's a real benefit of publishing your paper in an open-access journal. BioMed Central made the full text of all their published articles available for download as XML files, which means that all the sections are marked up and machine-readable, including the author names, titles, PubMed ID numbers and bibliographies. Running a small Perl script through these files, sending Trackbacks from one article to another, lets HubMed now display the full list of references for each article - in both directions.
In other words, anyone looking at an article (such as this one) cited by an open-access paper, can click on the 'References' link, then follow the 'Cited By' link to the citing paper (this one). Which will, of course, increase the visibility of the open-access paper (which is also free for anyone to read). From here you'll also see a further 40 outward reference links, each of which can be followed in the same way.
This is a great resource, previously only partially available through a costly subscription (and gnarly interface) to ISI's Web of Knowledge, and a lead which I hope commercial, paid-access publishers will begin to follow as soon as possible.
Update: I should have added that PubMed and PubMed Central/BioMed Central also have papers linked by citation in a similar way - see for example this article in PubMed, which was cited by all these articles in PubMed Central, which themselves have reference links from the (freely available) fulltext back to PubMed.