I just discovered iCyte today. Similar to Diigo, iCyte allows users to bookmark sites, highlight useful text, and write comments. I introduced my students to Diigo this year as a way or organizing and keeping track of their online researching.
I must say, iCyte offers a smoother, more intuitive interface. Like Diigo, it's a browser add-on, but instead of a clunky line of tools across the width of your browser, it's a nifty little button next to the URL window. You can either open a side window showing your bookmark history, or click to create a new bookmark.
Creating a new bookmark pops up a window that allows you to tag the site and add a note. You can also highlight sections of the text that will appear when you go directly to the library. Very cool, and much easier than Diigo. Better yet, unlike Diigo the tools worked seamlessly when I tried them with databases. With Diigo, we had to figure out a rather convoluted work-around.
You can create several different projects, and your bookmarks can be either public or private...and shared, of course!
On the website, log in to "My View," choose your project, and you'll see the tags, the highlighted sections and your notes. Like Diigo, you can't organize sites into folders, but this is a great opportunity to teach students the value of tagging frequently and prolifically. If David Weinberger is right, hierarchical folders and files are 20th century thinking, and tagging is where it's at for findability!
Best of all, you don't have to look at all those annoying sticky notes on websites when Diigo is turned on!