Why not use Twitter's swelling brain to predict what people might be searching for? Especially since access to the public stream is free to the public.
Articles by Laszlo Xalieri
Consumer/user privacy concerns are no joke, as Google and Facebook well know. Your "don't be evil" policies are only as good as your data security, ability to extrapolate the consequences of your actions, and your immunity to the temptation of a stack of cash.
To maintain a large commercial base of users to sell down the river to your marketers, you still need to figure out what people are looking for and give it to them quickly. That, or give them lollipops.