I use Diigo to bookmark psychology websites I find as I surf the web. I have been using it for at least 18-months now and have found it to be an invaluable tool. Admittedly, I am a pretty low-key user. I use only the basic bookmarking function, and have the toolbar installed on my work and home computer so I can access my bookmarks in either setting. To my credit, I was brave enough to set up a PsychSplash Psychology Group on Diigo where I have been posting links to psychology sites for the last 12 months. You can access my public list here (with RSS feed here) and the PsychSplash Psychology group here (with RSS feed here).
Just the other day, they launched version 3 which has really expanded the collaborative, community and social potential of the site.