google maps navigation works, but you have to start the navigation with an internet connection (that is, if you start your route at say your house with wifi, navigation will guide you to your destination and will work after you lose internet connection.) It will require a wifi connection to change routes or start a new one. There are alternative navigation apps that work offline however.
As for google now, I believe you can run local commands and searches (you might have do download a pack for your language), but obviously you can't search the web.
Google's own navigation feature isn't good enough for regular GPS usage, unless they can one day stream internet access from the GPS satellites, because navigational guidance is the most useful and most needed when I'm driving. Hopefully there will soon be software smart enough to recognize voice commands and is able to function offline, so I can just *say* to the device, "Navigate to Central Hospital", and it'll be able to compute turn-by-turn directions from wherever I am, when it's dark outside and I'm in the middle of a highway.
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