Usability 
Real time Twitter search. Most of the top tech bloggers (Scoble, Steve Rubel, Jason Calacanis) are active on the Twitter micro blogging platform. If you want to keep up the latest web 2.0 trends you really need to use Twitter. Twitter Search offers an alternative to following hundreds of people on Twitter, which can be pretty time-consuming. With Twitter Search you can do a keyword search against all public Twitters for the topics and memes that interest you.
Twitter Search isn't really a mobile site but its small page size and minimal use of images let its basic search functions work even on the limited built in browsers of most phones. Twitter Search's advanced search options which let you filter by user, tag, attitude or language require Javascript and don't work on most phones although Opera Mini handles the advanced search with no problems.