An article by Ben Hammersley describing the various kinds of TrackBack variants leads to some analogies with already existing biomedical literature discovery mechanisms.
For example, hyperlinks out from articles are the same as the References section of a scientific paper, the TrackBack method used by HubMed is basically the same as the 'Cited By' feature of other reference databases, and the 'More Like This From Others' used on many weblogs is a kind of 'Related Articles' algorithm.
However, while the old methods of article linking required a centralised database of citation data and teams working manually to sort papers into MESH categories, these new linking technologies use a distributed method of categorisation, as individuals compile groups of related articles into small clusters. In theory, these many minor links will continue to grow and cluster in a self-organising network, as new methods of automated link analysis enter widespread use.
Incorporating both TrackBack and collaborative weblogging, here's 'Make A List': an easy way to compile and share a bibliography of medical literature on a particular subject.
After searching HubMed, select the articles you're interested in and press 'Display Checked Abstracts'.
Select the articles you want to include in your list (or use the 'Select All' button), then press 'Make A List'. You should get a pop-up window containing your list items. All you have to do is give your list a name, write a brief description that describes the contents of your list, then press 'Post'.
Your list will be submitted to the BioLog for anyone to read. TrackBack pings will be sent to all the articles included in your list, so that users of HubMed will know that those papers have been referenced (see the 'TB' link in HubMed search results).
At the moment, all contributors are named 'guest'. If you'd like to be identifiable as the compiler of your lists, send an email for your own username and password.
Have fun - here's one I made earlier.
TrackBack is now enabled in HubMed searches. You can see forward links by clicking on a'References' link. You can use this feature to notify users of HubMed when you've posted commentary about a specific paper elsewhere, or if it's included in a list of references.
A TrackBack-enabled Movable-Type bookmarklet will pick up the pingable URL from any abstract display page (reached by clicking on an 'Abstract' link). If you want to automate the pinging process, the TrackBack URL is "http://www.pmbrowser.info/hubtb.cgi/" followed by the PubMed ID number, eg http://www.pmbrowser.info/hubtb.cgi/12529850
Sam Ruby has written a nice clear explanation of the benefits of external comments and trackback linking.