I applied 8.1.1 to my iPad 3 today. Yes, it seems a little faster; doubleclicking the Home button to bring up the multitasking bar took about 1.5 seconds in 8.1, and now it's just about one second. That's probably around twice as long as iOS 7, but the multitasking display is a lot more complex in 8. Switching apps with the four-finger swipe seems considerably faster, too.
No problems so far, but then I didn't have problems before, except the slight delay in launching and switching apps. I feel it's important to update to get the latest security fixes--slight delays are insignificant compared to getting invaded by malware or having your passwords stolen.
Now, if I could only talk my wife into updating her iPad Mini...