Too much back swing (over swing)

Too long of a backswing can definitely be a problem. You will hear a lot of people here, pros and teaching professionals mentioning the benefit of shortening the backswing.  I wouldn't say that making a longer backswing should or would cause someone to lunge at the ball, I'd say it would make it more difficult to be consistent and most likely I would think your misses would be due to a failure of being able to close the club in time.  Is your miss typically a slice?

http://www.youtube.com/watch?v=IsZ5UakcBpk

Not a big fan of many of the videos I saw. This guy had good comments.  I'd also suggest when shortening be sure to get good shoulder rotation and cut down on how much you take your arms back. If you cut out your shoulder turn in an attempt to shorten your swing you're going to be in a world of hurt.

I think, "Rotate and accelerate" If I leave out one or the other it's simply luck if it ends well.

There are two areas where over rotating becomes an issue. As you alluded to, by over rotating your back swing, you actually change where in the aspect ratio your lever (club) is because the timing has a delay mapped in now, usually leading to some sort of hitch to gain the time needed to get back to the ball. The second area negatively affected is, that by over rotating, you are most likely no longer on a good solid swing plane, which coupled to that delayed position creates a need to release early, stealing distance through club head speed bleeding away.

If you think more on the terms of your swing's width is seen as a sort of reach back motion, and not so much behind you as sort of to your right, along your shoulder plane. Add width to your swing path, which adds a more manageable angle of attack. Build width, and gain accuracy. Gain control over launch angles.

Overswinging is caused by a few things

1) your turn rates are off between your shoulder and your hips. Usually this means that your hips don't rotate in the backswing early enough, and the shoulders get to much rotation, so when you finally do turn your hips your over-rotating

2) your head is moving laterally, this can cause you to overswing, because it lengthens the time your club is moving. If you keep your head still, you can not physically over rotate the shoulders because your head will stop it.

3) your left arm breaks down at the top of the swing.

Yes it can effect your transition, it can throw off the timing.

You can try a few things, work on it slowly. Maybe try to start the hips firing in the transition earlier. You can work on keeping your head steady. Work on your backswing with slow swings, stopping and holding the position at the top were your hips are fully turned, your arms are fully turned, and the club is overswung.