Diigo – I’m an active user of the del.icio.us social bookmarking service, but I’m frustrated by its limitations. A big one is that del.icio.us only provides a few characters with which to describe the pages I bookmark. I frequently run out of space trying to write a description. Diigo is social bookmarking for serious researchers. Users of its toolbar can highlight and annotate passages on bookmarked Web pages. People can comment on each other’s bookmarked pages and highlights. Essentially, the service creates group discussion around Web content. Anyone with the Diigo toolbar can see other users’ annotations and sites that choose to implement the Diigo protocols can provide these capabilities even to non-Diigo users. There are other innovatives features in this release, including a function that lets you create a PowerPoint-like slide show sequence using Web pages. I’m not sure I see much utility in that, but the highlighting feature alone could be enough to make me switch from del.icio.us.