I started using Delicious a few years ago after I had become fed up trying to organise my website bookmarks. I often want to bookmark A&D news stories, blog articles, technical papers and standards, etc., so that I can easily find them again when I want to read through them at a more convenient time or when I need to do research for a Wind River article or presentation.
The problem with web browser-based bookmarks is that this approach doesn't scale well for a large number of bookmarks. Web browser bookmarks can be sorted into hierarchical folders, but this can be counter-intuitive if you have inter-related subjects (e.g. safety and security).