The "IE8 is the new IE6" claims at least have some meat to them: IE8 is the last (edit: MS) browser running on Windows XP which means as long as Windows XP exists in significant numbers so does IE8, but this is nonsense: Firefox, Safari and Chrome are not going back into their hole, which means IE9 will not be an undisputed champion of anything which means IE9 will not be the last IE ever to run on Windows Vista and Windows 7 (unless microsoft decides to get out of the browser market entirely, but I don't see that happening).
Thus IE9 can not be the new IE6. It might not be the best browser ever, but IE10 will come next and improve it, and IE11 after it.
If you're grasping for parallels, IE9 is the IE5 of CSS3, not the IE6.