John369 said he has switched to 2.4 Ghz and has no problems. I have always had my router set at 2.4 Ghz for extended range and am having all of the wifi issues others are posting about. I'm not so sure that "slow wifi" is correct. I think it is intermittent connection issues. When it works, it works. A page will partially load plenty fast, the stop with the spinning circle. It might resume, but more often than not, I have to go to settings and turn wifi off and on, then it resumes or will connect when it didn't and will be fine for a spell.
I have 8.0.0 on the Air and iPhone 5, 8.0.2 on the Mini -- no difference.
Even making the wifi connection takes longer than it should. The circle will spin and spin after the device has indicated it is connected with a check mark.
Safari might be contributing to this problem. When a page partially loads and the circle keep spinning, I can go to another tab and do something else, but if I go back to the partially loaded page, the circle is still spinning. Any chance Safari is overwhelming the wifi connection? Even stopping Safari and turning the device off, then back on, Safari will still try to reload that incomplete page. Annoying!
In addition to a Nexus 1st Gen and a 2nd gen having no problems with wifi, other devices I have continue to function without issues, even an 3rd generation iPad with the last IOS 7 release. There is now doubt in this persons mind that IOS 8 is the problem.
I'm pretty much tired of debugging Apple's IOS issues. My personal iPad Air and Mini are practically useless devices. I think I might head to Costco today and but a Galaxy so I can have wifi access while this is getting resolved -- or if it doesn't, I might like the darn thing.