A recent post on the DD forum got me thinking a bit - the question arose as to what the long term effects of dead-lifting might be and if they were negative. This is a very difficult question to answer because there are so many variables to take into account.
Such as: Form - how is the individual's form on the exercise? There is a reason serious powerlifters and olympic lifters spend lifetimes trying to perfect their form on an exercise. (3 lifts in powerlifting and 2 lifts in OL)
Volume - What is the level of accumulated stress? Too much of anything can be a bad thing. When it comes to dead-lifting and other lifts (like the bench)- less can be more. The activity might not be the problem - how much might be.
Recovery - Ties into volume but needed an extra section of it's own. Is the rotation of volume and intensity (to be discussed below) adequate for recovery? Too much coupled with too often is an even worse situation.
Intensity - Chronic training to failure or high volume coupled with high intensity can be great ways of hitting the bottom of what an exercise has to offer. BTW - intensity is a percentage of your 1 rep maximum - going to failure may or may not be intense.
Outside factors - What else does the person participate in? Strongman, Highland Games, Skiing, Running, Motocross, or any number of "hobbies" can be the proverbial straw that breaks the camels back.
Habits - How we sit and sleep can be more powerful than the activities we participate in - Chronic stress in the body from positions we hold for hours at a time can ruin you more than any lifting activity.
Nutrition - Ties into recovery but needed it's own section - How well does the person fuel the body that they are demanding performance from? If the fuel isn't there the body will simply take from "non-essential" (hint there aren't any non-essential areas) areas of the body and create deficiencies that lead to breakdowns.
And that is just off of the top of my head - medical history, injury history and family history can also play a role in the long term effects of any activity.
In general - with proper form, and cycling of intensity and volume a person can dead-lift for a very long time without detrimental effects. I myself have come back from back surgery to dead-lift 535 (and climbing) and my squat is climbing - and this is three years post surgery. Not exactly long term - but stronger is better and intelligent training is a big piece of the puzzle.