When in survival mode, drinking a potion of invisibility doesn't work against new AI mobs like zombies, Skeletons, Creepers, wither skeleton.
Other Mobs that didn't have they're AI tempered with such as Slimes or spiders don't attack or notice you if you have the potion effects. This is an old bug since 1.6. Mojang please fix it because the potion is otherwise useless. Please, the minecraft community wants this to be fixed.
Thank You