for me. On a current-year MacBook Air.
Switching "pages" when viewing the store regularly takes about 10 seconds, vs. a second or two before the "upgrade", every single song preview throws up a dialog box that says "Opening URL – Connecting" and requires a second click anywhere outside of that box to (sometimes) start playing, and then after a seemingly random period the entire Store becomes responsive and requires a quit and restart.
Is anyone else seeing this? It's unmistakable, and so far, uncorrectable for me.