Delicious!

Social bookmarking as a research tool.  Interesting yes.  Efficient no.  I lost the better portion of my morning to creating stacks and then browsing other's stacks.  Delicious.com is great for browsing when you have some time to kill (use the Inbox) but isn't going to be effective as a pointed research tool.  As for creating a stack that will organize all of your research in a particular area, it does that just fine.  Add the accessibility factor and you've got yourself a powerful, portable portfolio of information relevant to you.  Of course, you could invest some time finding others with similar information interests and follow their stacks for updates and news you may have missed.  I think it is with delicious.com as with many of the other web2.0 technologies that we've encountered......you get out of it what you put into it.  The more you tend to use and frequent these tools, the more useful they become.