Let's forget about the z-axis and new interface updates, there are some major new features in iOS 7 that I'm sure a lot of people will want to upgrade to within the first month. (I predict faster adoption for 4/4s/5 users than we saw in iOS 6)

In decreasing order of importance (my opinion)

o Pre-Launch background Updating (Finally!) - I spend 3-5 minutes, every morning, and another 3-5 minutes, every night, downloading my Podcasts before my walk home. Annoying. Now, in theory - they'll download for me in the morning and night. Awesome - particularly as my iPhone 5 is happily sitting in an elevation dock at 100% power for most of the day, or plugged in at home for most of the night. It Will be interesting to see what developers do with notification launched background apps - hopefully it won't be abused.

o Airdrop for iPhone (Finally! How many times have I wanted to get a file/image/content off my iPhone onto my Laptop just before a plane took off)

o Swipe Control Center - another "Finally" - getting closer to android parity/rooted iPhone parity - I tweak the brightness/lock rotation/pause/play music and settings pretty often. This will length the lifespan of my home button (double click + swipe left to currently get lock + music settings)

o Enhanced Camera/photo management - looks really nice - lot of people will like this - even the die-hard Camera+/Instagram/Flickr/Google+ photo types. I do feel kind of bad for Camera Noir - their window was pretty meager. :-(

o iTunes radio - particularly for all of us who already subscribe to iTunes Match.

o Advanced Siri - I use Siri many times a day, looking forward to this.