Earlier today I installed an older version (6.0.1) of Endnote on my Mac so I could import my Endnote library from my PC at school (which uses the latest version). To my chagrin, the older version of EndNote could not import the newer version's library. I figured I could just save my library in an older format, but that is not an option. The best I could do was export to a text file to import into the older Endnote on my Mac. This means that if I want to be able to keep my libraries consistent between my school and personal computer without shelling out another 99 bucks for the latest Mac version of Endnote (and without having to run Windows via VMware), I'll have to constantly export and import text files. The better solution: Zotero.
Zotero is a free, open-source bibliographic organization software that works as a plug-in in your Firefox web browser. Not only can you import libraries from some other competitors (by first exporting as a Bibtex file) but you can also directly add references from the web. Endnote can add entries from the web as well, but only if the site supports downloading into an Endnote format. With Zotero, you simply click on the icon next to the reference's url (or select which references you want from a folder that pops up if the url contains more than one reference) and it is automatically added to your library. You can also add entries manually and even link to PDFs, just as you would in Endnote. Now I can just share the folder that my library resides in (or check it into svn) and easily sync between computers without having to export/import all the time.
A feature that Zotero has the Endnote does not, is an easy locate feature for your references. I can click on a entry in my Zotero library, and it will automatically locate the reference online for me. By default, it uses OCLC's OpenURL Gateway as the link-resolver, but you can easily substitute your institution's own resolver under preferences. I found UNH's resolver using the WorldCat Registry.
Here are the results of me trying to locate my journal article. All I did was click the "Locate" button, and the resolver finds the link on my library's server. However, since I am currently off-campus, I cannot access the full-text online:
Update: I forgot to mention, that just like EndNote, Zotero can integrate into Microsoft Office for citing while you write. Unlike EndNote, it also integrates into OpenOffice and NeoOffice. Sweet, eh?