Yeah, I usually will start my Google searches in the Omnibox, then use the search bar on the page when I needed to find something new. In those use cases, instant is incredibly useful.
And it moves the design closer to the horrible design creeping into applications today: instead of designing for every device, too many apps are designed for the worst platform, which is mobile. Capital One just redesigned their entire site for mobile, which added a lot more navigation/clicks for web users. That's just inferior design. Actually, it's not even design, it's just inferior hack layout.
We live in an era where original web page design was horrible, and somehow we continue to make pages harder and harder to use. There's a pervasive myth among app designers and startups to just 'remove' functionality instead of actually delivering smart functionality. Simplifaction for ease of use is geat, but most simplification is just reducing an app to a single button and just makes real functionality harder to use. Omnibox falls into that trend. Make the search results better, get rid of spam, and stop spending even one second writing code to move the text input around inexplicably.
Good design should be invisible - I shouldn't notice it. Moving elements around after I've started interacting with them is just unnecessary annoyance with no benefit to me as a user. I don't want another crappy universal search bar, which is all this is. I just want to enter a search and move to the next page, so I can try and sift through the crappily selected results Google spits out. I already know Google's results are going to be poor enough I'll have to wade through them, why slow me down up front?
And so on.
You can easily switch to a different new page or use the address bar from the beginning.
What solution does this solve for me, the user, to have to determine that in this one instance, the textbox can't be used, but on literally every other application out of millions of web applications, text boxes work correctly?