I run a long game each month for my regular gaming group. This past weekend we played for almost 9 hours. Of that time we had 3 combats, one was a short 30 minute ambush. The second was a knockout, drag-out event against a green dragon that lasted about 1.5 hours, and was the most fun we've had in a combat in a very long time. The third was a defeat for them in which they knew they were headed into a TPK before initiative was even rolled. Instead of walking away they decided to fight anyway. They surrendered when 4 out of 7 were unconscious and dying that combat was about 15-30 minutes.
During the session they discovered that they are being hunted by a powerful enemy in the feywild, that the Harken Forest is being overrun with goblinoids, that the green dragon was threatening the fey of the forest. They made an alliance with a bandit "king" and traveled from Harkenwold to Fallcrest as guards for a priest that is relocating to Fallcrest.
The majority of the session was spent in roleplay interaction - talking with locals, getting info on the road ahead, travel, discovering the feywild enemy (combat), getting charmed by a fey creature (leads to combat with green dragon), "negotiating" with the fey of the forest (TPK potential), negotiating with the bandit "king", getting to Fallcrest, helping the priest settle in, and looking for leads in Fallcrest.
This was a most enjoyable session, and we had about 1/3 of the session in combat. However, combat was exciting and had purpose. Next month they adventure in Fallcrest, and we'll see what happens then.
My "perfect" mix of combat to non-combat is about 1/2 to 1/3 combat. I never like to have a higher ratio that that. Our combats are very non-conventional with the players doing all kinds of "wacky" things instead of concentrating on looking at "powers."