The reference has been bookmarked by 6 people, using 15 tags, some more popular than others. The tags and users are linked to Connotea.
This service is can be accessed at http://bioguid.info/services/connotea.php?uri=<doi here>, for example http://bioguid.info/services/connotea.php?uri=doi:10.1038/437477a. By default it returns JSON (you can also set the name of the callback function by add a &callback= parameter), but you can get HTML by adding &format=html. The HTML is also included in the JSON result, if you want to quickly display something, rather than roll your own.
Basically the service takes the DOI you supply, converts it to an MD5 hash, then looks it up in Connotea. There were a few little "gotcha's", such as the fact that the Connotea user may have bookmarked "doi:10.1038/43747" or the proxied version "http://dx.doi.org/10.1038/43747", and these have different MD5 hashes. My service tries both variations and merges the results.