I upgraded my iPad 2 to iOS 8.1. There are occasional glitches and some things seem to take slightly longer to respond, but all in all it's not too bad.
Safari, unfortunately, is next to useless if you're using more than a single tab. Crashes don't seem quite as frequent as they were in iOS 7, but switch back to the other tab and the page reloads, every single time. I've switched to Chrome because this was getting too frustrating.
One interesting thing is how there is some framerate drop in transitions and overall things don't feel as snappy as they used to. Sometimes you do something, in settings, and it just sits there with no indication that it's working. It's something I've observed even on the iPad Air, although it's obviously less prevalent. I find it ironic considering Apple devotes have long been critical of the same thing in Android. In fact, in terms of overall performance my iPad 2 feels a bit like old Android devices. Serviceable, but not great.