Enemy Spying on the player's cities

Other than stealing techs, what other infos would the civs gather?
I assume they can view my cities and units near it, but would they use any of these informations strategically?
As I gather informations about their army's movement against other civs, would they somehow gather infos about my own troops?

I'm guessing they have a chance to 'overhear' your diplo meetings with other civs- for example, if you ring up Montezuma to ask him if they'll join you in DoW'ing Napolean, and the french have a spy in your capital...

What you are building, and what you have stationed around that city.

smallfish said:

What you are building, and what you have stationed around that city.

Click to expand...

Yes, it is quite handy to use to check if your closest competitor(s) are already building a wonder that you badly want, or not. I think it even shows how many turns they have left on construction. Of course, they don't always build all wonders in the capital, so it's not a sure thing if you just have a spy there- but you can move your spy around to a different possible wonder-city every turn, if you really want to find out.

I fully expect that the AI civs already have full view of your territory and your units at all times (as they clearly act on information they couldn't possibly have if they played without cheating), so I doubt they'd learn anything extra from having a spy there.