Popularity of online reference managers

Now that we have a number of online reference managers to choose from, I thought it would be interesting to look at their popularity – both in absolute numbers of visitors and the in changes during the last 12 months. Online tools such as Compete allow everybody to do just that, and their basic functions are free to use. I've picked unique visitors, but there are of course other statistics to look at, including total number of visits.

CiteULike is the most popular online reference manager, and it is obvious that the announcement by Springer to sponsor them last August has helped their site traffic. Only CiteULike and Labmeeting show a significant increase in unique visitors in the last 6 months.

The statistics are more complicated for tools that include both a desktop client and online database (Endnote, Mendeley, Zotero) and these numbers should be interpreted with caution. I've included RefWorks in both graphs for better comparison. It is probably safe to say that both Endnoteweb and the online version of Mendeley are not as popular as the online only reference managers in the first graph. This could either mean that online only tools are far more popular than desktop applications (which I doubt) or that most references are still primarily stored in desktop programs and not shared online. Something that Eva Amsen already described last year (How to get scientists to adopt web 2.0 technologies). To put these numbers into perspective: ncbi.nlm.nih.gov (the home of PubMed and other NCBI databases) sees about 2.5 million unique visitors a month.