Question: I picked up the 2018 15" MacBook Pro recently, and right away I'm noticing the slightest amount of input delay on the keyboard. It doesn't always happen, but it's noticeable when it does - the typing cursor sometimes visibly lags behind when I'm typing.

It seems like it's happening a lot in Chrome specifically, though it happens in other applications. I could just be using Chrome a lot more than other applications.

Sometimes I can't tell if it's even input delay or just general slowness, for example when switching windows with CMD+TAB sometimes the window change animation is slower (it looks like I can briefly see the current window go from opaque to semi-transparent).

Has anybody run into the same problem, or does anybody have any ideas on how to verify whether this is happening? I notice it very clearly when I'm using my Mac, but since it's so unpredictable I'm skeptical of how reliable my observations actually are.

Answer: 
I think I remember a problem from long ago related to the Dock. Try opening /Applications/Utilities/Terminal, then executing "killall Dock" (It comes right back). This may just be a workaround and you might have to do it whenever you experience the problem.
Yes, the keyboard lag exists, you're not imagining things … nor are you the first to notice this behaviour. This fluctuating-delay happens because there's a T2 chip in the way, and the keyboard and trackpad are processed by the T2's own BridgeOS first before reaching the rest of the system that macOS can see and have influence over. Oh, and before you ask, using a Bluetooth keyboard is not going to be faster.

Sadly, until Apple actually acknowledge this additional annoyance caused by the T2, nothing will be done about it.