It really depends on the kind of shot and what conditions allow. That's why I answered in terms of focal lengths.) Shooting around the 65-85mm effective range is generally considered the most natural and most common, but if you want to flatten the image more, you can push it out to the 105-155 range. There are also some shots that work well in the 24-50 range, particularly when people aren't directly facing the camera or when you really want them to pop out from the scene and have maximum background blur with a short distance to the background.

I wouldn't describe the look up close as caricature or funny, but it is certainly a different look. It also generally seems to help if there is just a bit of barrel distortion to give it that slight fisheye look that makes the facial features appear to stand out less. Some of my favorite photos I've taken of my wife are actually shot in this range, but they are more face and neck focused, but it gives them a very intimate feel like you are right there with the person (that is if you can pull the shot off without facial features being a distraction.)

I also find I tend to like being fairly close for at least a couple of head and shoulder kiss or pre-kiss shots at weddings. This is again because it benefits from the intimacy that the close angle gives and since they are facing each other, noses stand out less. Again however, exactly how you compose and angle the shot is key to making it work when working in that close and it certainly isn't for every (or even most) shots.

As far as physical distance goes, I'd estimate I'm often within the 3 feet to 6 feet range though depending on the type of shot I'm getting though. 10 feet or 12 feet for more body or full body.