Google Mobile Search started to add a lot of features from the web search. After adding a mobile version for image search, news search, Google Maps, and testing mobile ads, Google shows onebox results. I could see a onebox for news triggered by popular queries like "Bush", a onebox for local results triggered by queries like "pizza in NY", short definitions if you start your query with "define", stock quotes, weather information and movie showtimes. Unfortunately, Google Calculator is not yet available.
These instant results are especially useful on a mobile phone, because most people don't want to visit a lot of pages to find simple answers.
To try Google Mobile Search, go to google.com on a mobile phone or a PDA, or visit google.com/xhtml.