The online social software services like del.icio.us let us do a remarkable thing. They create another good reason to store our data online for all to share. I can't tell you how many times I've made terrific discoveries because of del.icio.us/popular or Blinklist. And then added those discoveries to my own bookmarks, further increasing the public pool of knowledge. These relevance engines really do make excellent use of the data that we publicly conglomerate on these types of sites. The point here is that the value of software and data online is often much greater than the value of software and information offline.