The number of real time search engines is increasing. Yesterday, two new engines joined the race. CrowdEye is from Ken Moss, who ran search engineering at Microsoft and built the new engine himself. Collecta is from Gerry Campbell, who was a search executive at AOL and Reuters, as well as an adviser to Summize (now Twitter Search). OneRiot who is run by Kimbal Musk and my old friend Alessio Signorini. Other engines are Topsy, Tweetmeme and Scoopler, not to mention Twitter Search itself.
This reminds me the old times when Excite, Lycos, Altavista and a lot of new-comers joined the search race -- back in 1997. Search is alive and kicking with new exciting stuffs to play with.
I would expect more and more academic publication on real time search problems, such as real time ranking.