Assuming these sorts of things about your users' intent causes big usability problems. Trying to predict how users will use search usually ends up more frustrat

Assuming these sorts of things about your users' intent causes big usability problems. Trying to predict how users will use search usually ends up more frustrating than not for many people. Most people who use these tools don't have a working mental model of how search engines work, so they can't troubleshoot easily if your expectations and theirs don't line up. This is exactly the sort of "smart" feature that developers crow about all the time. Unless you have some way of predicting how individual people will use search boxes then you're much better off with something more general.