The bookmarking and reference service I use most is adding a show-and-tell slideshow feature. Diigo lets you mark up Web pages, then share and export your notes. Its new WebSlides, in closed beta testing, will enable you to create narrated presentations of Web pages that you've saved and annotated.
Diigo is meant to be more practical than something like StumbleUpon, a fun way to discover new sites. Diigo Vice President Maggie Tsai touted Diigo WebSlides at the Office 2.0 conference today as an ideal tool for teachers. Her demo showed off handy-looking recording and playback controls for making presentations out of your saved pages and then sharing them with groups of other users. The slide shows also display text you've highlighted or notes you've taken on bookmarked sites. Unfortunately, you can't test WebSlides yet; only a beta wait list sign-up is available for now.
I use Diigo instead of Delicious because it has more research-friendly features, and it can simultaneously save stuff to Delicious, Newsvine, and other services. Diigo's toolbar and pop-ups could be easier to use, and I wish it could annotate PDFs. Still, I'm hoping that more changes will continue to come along as the beta service matures.