In Civilization 4 you can see a score for each AI, which breaks down the reasons for their attitude towards you. Is there something similar in Civilization 5? I'm trying to work out whether it's worth returning a recaptured worker to its original civilization, but I don't think I have enough information to make the call.
Unlike civilization 4, there is no such numerical breakdown. The next best thing -- civilizations will either show up as "Hostile", "fearful" or normal. Normal is the default attitude.
I'm not quite sure what causes "hostile" or "fearful" (and note that hostile isn't exclusive to wartime) but you will quickly recognize these from the random insults (if hostile) or random compliments (of fearful) that the other leaders throw your way, as well as the other civ being listed as such on the diplomacy overview.
Since version 126.96.36.199 (15th Dec 2010) an AI player's attitude towards you (eg, Friendly, Guarded, Denouncing, etc) is always visible when conversing with their leader and on the diplomacy screens, and when hovering your mouse over the attitude you will receive a tool tip containing a breakdown of the leader's current thoughts about you.
While this is much closer to how Civ 4 displays an AI's attitude, but unlike Civ 4, no numeric values are given so you cannot see the relative weight of these thoughts, only whether they are positive or negative.