I have been playing with my new rMBP now for about a week. I was enjoying Safari in ML. I could not really notice any lag. There was extremely minor pauses on the odd site, that I took to be more bandwidth issues. I have my rMBP (2.6/16/512) running in the top end resolution - 1920x..... I have just been trying out the latest stable build for Chrome (Chrome Canary was buggy and flashy). The new build of chrome is incredibly fast, way faster than Safari. Most things are instant relative to Safari and relative to just the general definition of the word "instant", and now I can not go back. I also like the fact that I can set Chrome to 150% magnification and it does this for every page automatically. No doubt there was some way to do this in Safari, but I could never find it. I loved my rMBP before, but now, this makes it even better.