I have also been using iTunes above everything else to organize my music, but the Zune software has some really great organizing features and now I'm using it more than anything else. The Zune software automatically uploads music into my library as I'm downloading it, which is a real plus because sometimes I'm downloading so much that I leave one or two songs out when I upload them to iTunes (although rediscovering these songs months later is always a pleasant surprise!). The Zune interface works basically the same as Coverflow, only without all the pretty animation. Under the "artists" view you can drag and drop whole albums onto playlists, which are kept under one individual icon at the bottom of the screen (you can also drag and drop onto the "Now Playing" list the same way). The same drag and drop function is used for syncing with your Zune, which seems to be better than iTunes but I never owned an iPod so I don't know how syncing really works with those.
Also, the best organization feature (I think) of the Zune library is its ability to find information about the songs you have. I have many individual songs by rather unknown artists, and I'm a little OCD about having album information for all of my music, and I was able to match many hundreds of songs to albums (automatically, I actually did nothing) on my Zune software that iTunes could never discover for me. Also, it's easy to look up album information quickly without having to drag through the entire music store with the "find album information" feature.
As for playing songs, the Zune software does NOT automatically jump back whenever the song switches. The "artists" view (the one I use the most, obviously) has three panes--artists on the right, albums by cover in the middle, and songs on the left, and you can easily navigate through all of these and get back to your entire library by clicking the number of artists up at the top of the artists pane. It also has a handy back button to navigate backwards through menus, which is great, especially if you're switching back and forth between your player and your library.
As for navigating while driving, I don't really know a whole lot about that because I usually just stick my player on shuffle and go with it, but the touch pad is easy to use whether you prefer to slide or to click (sliding your finger across the pad and clicking one side perform the same function). Also I know that the Zune's screen is bigger than the iPod Classic's and many of the menus have a larger font as well.
And as for the accessories, this is one huge disadvantage for the Zune. Unlike the iPod, there are very few Zune-compatible products out there like car chargers, docking stations, and AC adapters, and none that are specifically for the Zune (many use USB connections). In other words, you're pretty much stuck with shelling out the name brand price for any accessories you want for your Zune, which was a big hit for me. I would LOVE a car charger, but not at $50-60.
Hope this helps! I was given a choice between an iPod Nano or a Zune for an mp3 player and I am extremely happy with the Zune's interface.