Mares and geldings together - opinions?

My gelding is going to be moved to the mare field soon. It will be a smaller herd (5 or 6 mares) and he is moving over with another gelding he has been with for a while, and who he is out with alone at night, so they are buddies. The herd size/proportion to hay is better for my guy :) But is there anything I should be cautious of? They shared a fenceline (mares and geldings) and one of the mares is from the farm where he came from last fall. I should also mention he is super quiet, low man on totem pole but will cow kick if someone bothers him a bit too much.....but I'd classify him as somewhat passive/lower on totem pole. The mares are nice as far as I know, and very calm.

Will his behaviour change, riding, etc? I'm sure there will be a transition period....how will this affect him, and do you board mares/geldings together? Thanks :)

I don't have problems with mares and geldings being together, unless, of course, the gelding will react when the mare(s) are in heat. If he starts to get weird around them and acting (or will) mount them, then move him right away.
That's about the only thing, though. Just keep a watch out, espically when they (mares) are in season.
But, if he's fine, then it shouldn't effect him (unless the mares are in heat and he reacts), in my view, but if it does, then move him.

My horse lives in a mixed group (including him 3 geldings, 2-3 mares) and I've never had any problems that wouldn't exist if he was kept only with geldings.
I don't think you should have any major issues, but I would keep a close eye on them the first few days and the first time the mares come in heat to see how the geldings react.

at the barn where I board there is a mix field. There's maybe 7 geldings and 2 mares and they do fine, no real fights or anything like that.

I wouldn't worry too much on it. Maybe for the first few days keep an eye on the field to see how he's mixing and how the mares are mixing with him...but I don't think there will be too much of an issue.

In a wild horse herd, there's usually one stallion, and the rest are either mares and then foals...so I'm sure the gelding will take up the "stallion" position...at least that's what my friends horse did when he went with a bunch of mares

Really, i don't see why people separate them. Its pointless to me, when i tell people who separate them that its pointless, they get all defensive. Its odd, naturally they are mixed. They don't have "mare herds" and "gelding herds". So why segregate them to the point where they are put out with their own sex. I don't understand it.

my gelding has always been turned out w/ 2-3 mares and has done great. and there's a difference in a herb between defending yourself and being a bully.

my mare is in with 2 other mares and 2 other geldings and there fine...although when i got my first gelding he tried to mount one of the other geldings

I agree. I know someone who has each horse in a little pasture - she doesnt let them together at all because "then the will run around and can get hurt"

Ummm... they are HORSES!! One day her TB Gelding was running around in his little pasture and she actually ran out there to stop him from running.

My mare is mixed with geldings; I don't see any problems.
Sometimes, some of the geldings will react when she's in heat, but nothing too major. I think it's fine. ;)

My gelding never acts bad when he's with mares, I couldn't see it affecting anything.