Twitter acquired Summize in last July. Summize was a popular service for searching Twitter and keeping up with emerging trends in real-time. Later Summize was renamed as Twitter Search and it was added as a sub-domain for main twitter.com site.
However twitter yesterday announced that now Search and Trends will be part of signed-in home pages. This feature is currently under testing and so it is available to a limited set of accounts. Later on it will available to all users. Most people will not see this test, just a small, random subset.
Searching over Twitter messages is like a filter for what is happening right now—it's an interesting look into the real-time thoughts of people and organizations around the world. Whether you're curious about something specific or you just want to browse the trending topics, Twitter Search adds a new layer of relevance.
Only accounts that choose to be publicly accessible are included in Twitter Search. However, more than 90% of the folks who use Twitter have decided to make their accounts public.