So I now have an iPhone 6 - after sticking with my old iPhone 4S for three years the new 6 offered enough difference to be worth the upgrade.
The migration was trivial and took less than one hour, with all the apps still apparently working and nothing more than a few logins to reset.
For the phone, the highlight is obviously the bigger screen. I didn't really think the 4S was small, but wow the 6 is just so much better in that department, with even more clarity and so much more text visible. Reading news or looking at photos is a vastly improved experience, and I didn't even feel it was a problem before.
In terms of the hardware, it feels solid, and the (optional) leather case is very nice to hold. Camera is significantly more responsive, and the fingerprint ID works pretty well. The size is OK, obviously a lot bigger but not so much it feels inappropriate for a phone.
The only thing I've noticed is that quite a lot of apps are obviously not yet adjusted for the new resolution, so the graphics feel blown up and a bit bold. It's a bit like using the 2x view of an iPhone app on the iPad but not as bad.
Update 17 Oct
The Belkin Charge+Sync Dock works with the iPhone 6 with the leather case on. I think without the case the phone would be too thin and lean back uncomfortably far.