I have to totally agree with this important document about teachers leaving out some of the most useful ways to define words - -I teach my students to define in google AND on their cell phones. Why not? 10 seconds to text to google AND get an answer -- several minutes to use a dictionary.
This organization had people vote on the top elearning tools, while I'd put Diigo FAR AND ABOVE higher than delicious, a lot of people just haven't tried it yet. (I still send diigo links through to delicious anyway.) Some interesting items on here.