1) It's a search box. Stuff not typed in the search box never leaves the machine (unless you count things that do by design, such as web browsers and email, obviously).
2) It's plainly obvious the first time you use it that results are coming back from the Internet. No real user is going to be misled into believing that searches are local. This makes it no more a privacy violation than the default Google search box in Firefox.
2b) There is a prominent notice saying so. If you don't think it's prominent enough, see point 2.
3) It's a search box that didn't exist previously. Canonical invented it. I think it's reasonable for Canonical to create a "search the universe" mechanism on the desktop. Fair enough if you don't like it, or don't want to use it. It's trivial to turn it off (there's even a global Privacy Settings dialog) or to use other searches. But that doesn't suddenly make it a privacy violation; nor the results of your search "ads".
Edit: I should have expected the downvotes. I notice, though, that the downvoters are unable to actually respond to my argument.