Google has just updated its free iOS Google Search app to include its Google Now service—a personal service that offers users potentially useful information based on their habits, location, and previous interactions with Google's many systems.
Now is different than Apple's Siri in a number of crucial ways (for example it doesn't have a personality and it doesn't require too many deliberate user-driven interactions), but it's seen as Google's main rival to one of iOS's flagship systems.
While Now won't work in quite the same automated pop-up way it does on Android, the move is definitely a play by Google to steal away web traffic from some of Apple's own systems. Google has recently seen Facebook offer an equally subversive app, Facebook Home, that also in some ways moves the OS experience out of its creator's hands.
Apple has recently posted numerous job openings in what seems to be a concerted push to develop Siri much more than it has been thus far.