Short story: Google Chrome installs something called Keystone on your computer, which nefariously hides itself from Activity Monitor and makes your whole computer slow even when Chrome isn’t running. Deleting Chrome and Keystone makes your computer way, way faster, all the time. Click here for instructions.
Long story: I noticed my brand new 16″ MacBook Pro started acting sluggishly doing even trivial things like scrolling. Activity Monitor showed *nothing* from Google using the CPU, but WindowServer was taking ~80%, which is abnormally high (it should use <10% normally).
Big, big props to Loren Brichter for making this website and thoroughly documenting this issue.
Loren is a former Apple employee who created Tweetie and Letterpress earlier this century. There is a Wikipedia entry with more information about him, written from somewhat of a fan perspective.