I experience no slow down of navigation on my phone. It runs just as quickly as it did the first day I took it out of the box.
You do if you have to wait for an additional animation to star and stop. It's just not possible to experience no slowdown in navigation when you are waiting an additional tenth of a second for an animation to complete when you weren't before. That's a tenth of a second slower.
I know most people here don't care. It's not like it's horrible looking. I'm really surprised at the number of people who don't even see this happen. It's certainly intentional and was meant to be included in the OS.