Running could be overall good for you and not harmful to your joints ...
IF
you are not overweight, have not had a previous knee joint injury/known osteoarthritis already, and don't lean backward so you have a pronounced heel strike.
Fairly strong leg muscles from doing closed chain weightlifting (squats, deadlifts) seems to actually be protective of joints - at least not if getting into very high weight lifting.
Here's the conclusions of a fairly recent review article that may be of interest:
"Conclusions:
Impact loads [jumping] are the most likely to result in injury to articular cartilage.
Having well-developed muscles decreases the loading on the cartilage and thus has a protective effect.
Animal research suggests that exercise--at least when done in the form of running--is not harmful to normal joints even under high loads and over long distances.
In contrast, similar exercise of an injured joint leads to arthritic change.
The literature suggests that in humans, athletic activity is associated with a slightly increased risk of osteoarthritis.
Athletic individuals seem to tolerate similar radiographic levels of osteoarthritis with less disability than nonathletic individuals.
Joint injury is the primary factor that increases the risk of arthritis developing in athletes. [More likely in contact sports.]
Activities that maintain flexibility, muscle strength, and coordination protect the cartilaginous surfaces and help to maintain joint function in joints that have already been injured and in which arthritic changes have developed or are developing. The forms of exercise that meet these criteria include
bicycling, weightlifting (with emphasis on closed-kinetic-chain exercises), and pool exercises.
A good program to start with is an exercise bike with the seat positioned high and with resistance set to a low level. After the patient is able to spend 20 minutes on the bike, the seat may be lowered to deepen flexion, and the level of resistance may be increased. The patient may then add leg presses using a low weight and with a high number of repetitions (start with 20 repetitions at a time). Patients may progressively add weight to the leg press until lifting to their tolerance. I tell them to avoid knee extensions despite the fact that these machines are found everywhere. Reactive forces on the patellofemoral joint exceed body weight, even when light weights are used. For patients without access to exercise equipment, straight-leg raises are a good start. Wall sits are a substitute for leg presses, although it is often difficult for patients to start out with wall sits because they cannot exercise using less than their body weight. Patients should also work on a stretching program to maintain full extension of the knee.
For patients who have suffered a significant injury to the knee but who do not have arthritis, activities that include prolonged, repetitive impact (eg, distance running) are not the best choice for maintaining fitness. Other activities that the patient enjoys and that maintain physical strength and flexibility are probably acceptable if they do not cause pain. The best choices are bicycling, swimming, and weightlifting. Runners usually find this recommendation difficult to accept; many dedicated runners do not feel that any other activity makes them feel as good as running does. Sometimes a difficult decision must be made, however, and they must recognize that they exercise for many reasons and that the possibility that arthritis may develop may be offset by the cardiovascular benefit and the sense of well-being that they get from running. Doing any exercise--even one that is not especially recommended--is better than doing no exercise. If the choice were running or nothing, I would run."
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http://xnet.kp.org/permanentejournal/Fall00/Osteoarthritis.html
