Well so far the Z1 is dead-on accurate. I try to trip it up, but each time it re-route itself within a few seconds. It even pronounce most street name via voice when you're approaching a turn e.g. " In 1/2 mile turn left on Main Street" - much more convienient and accurate then "turn left in 1/2 mile".
DVD resolution is pretty good. It's not a hi-def screen or anything, but very nice. There is some glare in direct sunlight. And of course, you can't watch while driving...at least not until someone figures a way around this safety feature. I did ask the installer to ground the parking lead..but it still doesn't let me watch DVD's while driving.
Map is very detail. For instance it shows what lane you should be in on the freeway when approaching an interchange. It gives voice prompt for turning within 1/2 mile of major intersections. There are multiple map views (map view, twin view, driver's view, and a cool telemetry view). You can also tell it to overlays POI such as gas station, ATM's, shopping malls, etc... It even have special icons for popular retailers such as Walmart.
Well, there are tons of features on this thing that I haven't even play with yet. One thing it doesn't have that I wish for is RDS. But I guess when I get the XM adpater, I don't really need RDS.