Process isolation:
Run Chrome
Open a lot of tabs
Open one with a HTTP auth that brings up the native browser login dialog
Switch to another tab
Close the one with the dialog
Result: whole browser crashes.
Moral: process isolation does not mean better user experience.
Like I said a lot of times:
IE 6 is still officially supported
IE 9 is not available on XP
This is why Microsoft is still crippling the web.