There are tons of graphical glitches and delays. I did a clean install.
If you play a video in safari, and rotate it, the GUI will go insane. Try it.
Sometimes when you send a text, the message bubble will be invisible for a split second.
Pulling down notification center had a delay a lot of the time.
Things crash left and right.
1) Mine rotates a little weird. Video doesn't stay centered but doesn't go insane.
2) Sometimes this happens - doesn't make it unusable tho.
3) Do not see any delay in doing this.
4) Apps will crash until they are updated to support iOS 8.