You can, of course, also enter a DOI in the post publication dialog or by providing accordingly formatted BibTeX fields as described a an other blog post. Publication references in BibSonomy containing DOIs can be easily identified in every resource list, as the corresponding entries contain a direct link to the referenced resource:
With our last release, we additionally added the DOI link to the details page of each publication containing a digital object identifier, allowing to easily navigate to a resource of interest:

Stay tuned to learn more about new features and background information - Happy Tagging!
.folke