A couple of things that I noticed when playing a recent game of civ.
1. You walk into a hut and you get a merc unit with a none support. That means that an enemy city is around very close to you. I got some mercs this way and slaughtered the Japanese in their infancy
2. Your capital is much more able to resist barbarian attacks than any of your other cities early in the game. I saw my pathetic warrior unit hold off an attack from 2 barbarian archers in my capital. No city walls (only 2700 BC!) and not a veteran even after the second attack. This is normally suicide on Deity level - don't try it with any other city. I tried it on other games and it seemed to me that the units in your capital have a defensive bonus for the first 20 or 30 turns.
3. Send your diplomats/spys into a computer city via a boat. They never seem to see it coming. They try to intercept your diplomat if he is on land moving toward their cities.
1. You walk into a hut and you get a merc unit with a none support. That means that an enemy city is around very close to you. I got some mercs this way and slaughtered the Japanese in their infancy

2. Your capital is much more able to resist barbarian attacks than any of your other cities early in the game. I saw my pathetic warrior unit hold off an attack from 2 barbarian archers in my capital. No city walls (only 2700 BC!) and not a veteran even after the second attack. This is normally suicide on Deity level - don't try it with any other city. I tried it on other games and it seemed to me that the units in your capital have a defensive bonus for the first 20 or 30 turns.

3. Send your diplomats/spys into a computer city via a boat. They never seem to see it coming. They try to intercept your diplomat if he is on land moving toward their cities.