Sometimes. If I'm close to getting a General, or if I'm gaining a lot of experience and not losing units, I'll just prolong the war because it's not a loss for me. If the AI has a defensive pact, this might be the best time to push without drawing others into a war.
Where I draw the line is when I feel like I'm going to lose units. I've sometimes made peace because I got one of my highly promoted units in a pickle and I want to save it.
Or when the AI starts rolling out higher-tech units (like if the AI starts rolling Knights and you still have Spears, peace is probably a good idea). I don't want to risk it.