I played around with the iPhone 6 and 6 Plus at a store. They seemed fine though the 6 Plus felt unwieldy.
iOS 8 seems to have more problems than previous versions of iOS. Safari and Facebook occasionally close for no reason (they did before, but it's more frequent now) and I had to do a full restore because the music app was completely messed up after upgrading to iOS 8. For example, if I was listening to Artist X and I went to listen to Artist Y, it would still display Artist X's songs, but when I chose any song, it would play one of Artist Y's songs. I've never had this many issues with an iOS upgrade before. It works better after restoring. However, I still can't scroll to highlight text; I can only highlight what is shown in the text field. In any case, it still functions well most of the time though I hope 8.1 fixes the issues.
I'm not sure when I'll upgrade to Yosemite. I just upgraded to Mavericks a few months ago (I haven't noticed many differences though it's slower than Snow Leopard likely due to the age of my MacBook Pro) so I may wait until Apple releases some updates and it's stabler. I expect a 21.5" iMac with Retina Display next year when Intel finally releases Broadwell or even Skylake. That said, I don't know how long my MacBook Pro will see heavy use so I may not even bother.