For me--and this could just be my device, as it has weird issues with other stock google stuff--I can't use Navigation or Google Maps offline (and yes, I have the entire area cached offline). I even tried starting something on Maps with wifi, just so I could remember the address, but as soon as I was out of network it stopped working altogether. When I try Navigation offline, it's stuck "loading" forever.
I use CoPilot, which works great. There's a free version, but it doesn't have text-to-voice or 3d maps (fine if you're walking somewhere, but impractical if you're the driver). For $10 you can dl the entire USA map, plus have TTV/3d maps + 1 year of traffic (useless on wifi N7's). Plus, you get tons of offline POI's (great if you're in an unfamiliar area and want to say, check out the local shops or go get groceries/gas)