Stand on the shoulders of giants [via del.icio.us]. Ranked by citations; appears to merge single results into one when the same PDF is present in different locations; gets results from pay-for libraries; use the author: marker to search metadata; includes books. Incredible. It looks source-based, like news.google, and they've included the major databases in the few fields that I know enough about to check. Already great, potential: huge. Abstracts? A better citation browser? Personalised (it's be useful, I need profiles to say I'm not looking for crystal papers when I'm really looking in sociology). Research tools and persistence. Presence. Trailblazing. APIs.
Gosh. I'm not sure it'll displace Citeseer as a paper discovery tool (ooh, there's a cool graphical browser I hadn't seen before), mainly because Citeseer has more detailed information immediately available, but as a way of getting a rapid overview of an area and to perform idle, broad searches, this seems to be a great orthogonal slice through academic space.