How many days of "actual combat" do you think an Infantryman deployed in support of OIF/OEF experiences over a year-long deployment?

Depends on unit and location. I think the intensity of the actual combat is much more pronounced.
But dealing with the day to day stress of hostile environment takes its own toll.

The real question is how many days are soldiers under a state of alert in a combat zone? Every day! Nobody likes being under a threat 24/7.

When I was in Afghanistan our COP was regularly attacked 2-5 times a day nearly every day for the 6 months I was there. Defining whether that would be combat or not depends, the Taliban were such shitty shots that most of us weren't worried about the mortars or RPGs. They fired an rpg at a fixed OP on the top of the mountain and missed. Now when we went out on patrols and regularly got ambushed is a different story.

I'm sorry but I would say that just having to do patrols, guard duty, GACs, and all the other crap you deal with down range all takes a toll on the body and mind......then there is the is the ever present rocket attacks....we took over 60 in a very short period....now because we did not return fire it was not classified as "combat" for medals....but as to mental health and well being I assure it sure felt like combat and i'm pretty sure if I'd been hit Mom and Dad would've been told I died in "combat." Anyway what i'm getting at it the threat of being killed on a daily basis may not be "combat" by some terms but you know ....it probably should be.....not like there are rockets being fired at Ft Bragg.......anyway moving on and hope this makes sense.

As everyone else has stated it depends how you define combat. While I was living on FOB Shank we caught 100 mortar attacks that hit the FOB in a 90 day period, for a total of over 150 rounds, most of which landed within 200 meters of where my unit lived and worked. I'm not sure I'd consider that combat but others would. I've also been on a deployment where I was on the road every day for over a month and was never attacked, is that combat? I'd once again I'd say no but other would say yes. I'd strongly encourage you to read LTC Grossman's books On Killing and On Combat.

Depends on location, time and year. When I say time I mean season

Considering that an enemy round travels at a couple thousand feet per second, even a heartbeat can be a lifetime, so even one day is one day too many.

That's an unaswerable question, unless you refine it to apply only to a specific unit or person. You've got way too many variables otherwise.

Only takes one to get you killed.

I keep coming with an of 310 days based off of the fact "life and death". Granted every moment spent in country is life and death. Yes, like some those have said mortar attacks on a FOB are days of combat. Granted you may not have had hardly any firefights or attacks, it's averaged out amongst the entirety and not just one persons/units expiernce.