With the cold winter we are having (at least in this neck of the woods), and since I do mostly warm water fishing (oh, I do make a few trips to the mountains for trout), the subject of water turn over is always of concern, especially if your a fisherman!
Since there's nothing I can do about it, I don't worry about it. I think the depth of the pond/lake plays an important role in the process as well as any movement in the water with feed creeks etc. Considering most ponds are relatively shallow (i.e. 25 feet or less in depth), I suspect that the water gets churned up enough to make this a non-issue for most of us.
don't quote me but I pretty sure the body of water has to be quite large and deep (over 40') to flip, other wise it doesn't.
Turnover happens in many temperate lakes, and in most cases, is considered a good thing. It helps to mix the water column which distributes the dissolved stuff that keeps things alive and thriving. I think the key is whether or not a thermocline develops. In shallow water, the water stays pretty much mixed so the thermocline doesn't form. When a thermocline does form, it acts as a density barrier. The water on top, stays on top and continues to heat up during the summer. Once the surface water starts to cool off in the fall and winter, it's density increases to the point that it overcomes the thermocline barrier and sinks to the bottom. That in turn forces the deeper (now relatively warmer water) up. Pretty much mixing the pot.
For some reason, I've always been fascinated by the miracle of nature that is water. It's the only thing I know of that actually becomes less dense when it becomes a solid. If it wasn't for that simple fact, lakes would freeze from the bottom up, which means many of the fish as we know them wouldn't exist. Maybe not something that is a big deal for you guys down south where the water never freezes, but I'm reminded every year up here when the lakes ice up. It really is a miracle that someone up there figured that out ahead of time and made things the way they are.