I like the option to trade techs, I feel like with it turned off I don't have too much interaction with the various AI, but with it turned on it really seems to make the game quite a bit easier. I think partly because the AI does not value its unique techs nearly as much as it should. There are a lot of great 5% type global bonus techs you can get off the AI for peanuts, and they really add up after a while.
I am not sure how aggressive the AI is about getting those techs from each other, but they really give a big advantage to the player. I have heard talk about adding another game setting to disable race specific tech trading, and I think that would help quite a bit, either that or have the AI a little more careful about giving away their racial techs.