Q u o t e: I first noticed this change in behavior beginning on January 1, 2009... and confirmed it on my Daughter's copy of WC3, ROC as well.
When playing against the computer in single player or local area network gaming, the computer can always see your base and units, anywhere on the map, as well as your allies. This did not used to happen - the computer had to creep for you, and could not go directly to you from anywhere.
I would appreciate it if somebody would confirm this on their copy as well. You can do this by selecting a large multiplayer map, build units and wait for them to come. They will no longer creep, but will head straight to your base. They will do this immediately if you do not level up your hero, or outbuild them quickly (Just build a hero and stand there... they will come directly from their base).
Furthermore, if you do the cheat to see them, you can see their behavior as they stalk you on the map - clearly they have no fog of war anymore.
It makes playing them on insane nearly impossible now - and it used to be fun.
I wish they would have an super-duper-crazy-insane-unbeatable-without-cheating difficulty.