Use in car? yes!
"I'd like to erm, do the arhm... ahh forget it" - types
typing is much easier for putting thoughts down "on paper", you can type just what you want to type, and backspace to remove mistakes. Bit hard to do that with voice.
I do use mine in the car a lot though, very useful for triggering the satnav, or starting a voice call when driving, you can keep your attention on the road (as much as possible, far more than if you were trying to load the maps app, type in a destination and set off the navigation).
"Ok Google, navigate to 123 example street" - damn useful.
And that's why it is used more in cars, even before you factor in speaking to it in public being embarassing, it's a hands-free method of operating the device, in a situation where you are explicitly doing something that requires use of your hands.
If you are just sitting there browsing, then your hands are perfectly free to interact.
I'd actually be happy talking to my phone in public, the voice recognition is actually really good, and mostly understands me properly - more than some people, as I sometimes slur words through talking too quickly and google still tends to know what I am saying.
The thing is that I find fingers on a keyboard to be a better utility for text entry, no matter how good the voice recognition is.