its fast.
but yes, fast is relative
if you compare it though to your average desktop computer that you'd buy from a major retail store, it'll be on par or snappier due to things like SSDs.
For your average computer user, it's going to feel like a very snappy powerfull machine. And there's no complaints. it's the fastest and most powerfull lappy i've ever owned.
But if you're a desktop user with a more customized experience, higher end parts and a machine built to be a powerhorse, You'll notice that it's not quite up to speed.
Things that really leverage multiple cores and really use up a lot of CPU cycles and memory will just not compete. Gaming is an example of something the MBA, while it can do, will never keep up. I'm sure we can all think of other examples where the power just isn't there.