I've seen people saying that the wi-fi functionality of Sync 3 isn't used for anything in the UK. But, in the past few months, I've had 2 updates to Sync 3 delivered over wi-fi.
First was a few months ago in my Edge, I started it up one day and got a message telling me Sync had updated.
The second was last night in my S-Max.
When I pulled on to the drive, when I got home after work, and Sync had connected to my wi-fi it popped up say that it was downloading an update. Going into the "Automatic Software Update" screen via settings showed which file it was downloading and a progress bar. I didn't see any progress in the few seconds I was watching and just got out and locked the car up as normal.
This morning when I started it up there was the message saying that Sync had updated. Settings showed the build number had gone to 19025.
I've only had the S-Max a couple of weeks and did manually download and update Sync and Maps in the first couple of days of owning it. Then I saw reports of a new Sync update having been released on 30th September. I've actually downloaded that on to a USB stick ready to install but, although the USB is in the car (not plugged in to anything) I hadn't yet had chance to do the update manually.
Checking my VIN on the Ford Sync Updates site shows that I am up to date so I guess I don't need to bother plugging in the USB now.