Avoiding random reboots
Appear for some users the random reboots (memory leaks) in the iPhone 6. This error has already happened earlier in iPhone 5, 5s and iPad Mini, Air and Retina. While not occur as often as before, still going for some users.
While there is no permanent cure, there are some tips:
Restart the iPhone 6
Master reset by: Settings> General> Reset> Reset settings.
Uninstall recent applications
Wait for iOS 8.1.