I think creatures should not only have a schedule but should also have a "desire to live". Dastardly persons and creatures you run across seem to always attack you on site, no matter how fearsome you look, and no matter how many of their friends you just ripped in two with a sword, fireball, or your bare hands. The one comment about how a giant in this game won't attack you on site if it isn't in the mood is the perfect example of what I want to see in all sentient creatures.
If you are in fact a level 20 dragon slayer in a set of Daedric armor then bandits, for example, should be able to think twice about attacking you head on if attacking you at all. For the aforementioned Daedric vanguard, Bandits could take a look, gauge the threat, and at the very most choose to let off a few arrows from far away before running from your now alerted presence.
Aside from custom dialogue, I don't see this being too hard to implement. You can have a threat level based on recently cast spells, types of armor you wear, your handled weapons, and even what level you are. Based on your threat level, creatures can continue what they're doing while keeping an eye on you or, in certain cases or at certain ranges, stop what they're doing and be looking at your actions until they feel they need to defend themselves or run away.
I think creatures who, aside from programmed schedules, look and act like they actually want to live would add a metric ton of positive realism to the game. Who else would like to see this implemented?