Been doing a poll on macrumors (cannot do polls here, my attempt was deleted by Apple hmmm)
Anway it appears about 20% of users responding have had issues with iphone 6's, most have had issue with 8.0.0 and problems not fixed maybe worse in 8.0.2. But 80% did not and that was my experience with my iPhone 6 plus worked fine with 8.0.0 and better for me with 8.0.2.
5% of iphone 5 users having problems with iOS 8.0.x. A small percent of ipad users having issues.
From what i am reading I am surmising several issues. The complexity of router configurations/hardware that apples growing iOS devices has to work with is growing and that issue. Just like Microsoft having to deal with variable hardware and its OS's now apple in terms of IOS is seeing same kind of issues.
Given that more iPhone 6's are having issues (20% give or take in my little sample poll so far) I think as someone here or elsewhere mentioned the new WIFI chip on this new phone is causing problems and when a router configuration/hardware not compatible with new capabilities and settings (often tied to what iOS 8.0.x does). But 20% having problems is not nice especially if you are one of those folks. I am not sure how apple can overcome testing more router configurations and settings but they need to figure this out in beta testing. I think they need a bigger hardware and combined iOS testing program (I will volunteer ha ha if I get my hands on new tech he he). I am not sure how microsoft deals with all the variables as it has alot of its own issues but this is not good for apples current customers and new ones as well.
I see a mix of new and old customers with issues, and this is not acceptable. I suppose some of the later can be chalked up to inexperience with iOS, and the setup of home routers (heck I see lots of ones people do not even protect, rename in otherwords they plug in and mostly go) but apple just having things that "just work" is ending as it expands into hardware variables and how they work with iOS.