Some final comments
I just wanted to wrap up my posts on kettlebell training by reiterating a few points.
First of all, kettlebell training is not a silver bullet. It is a form of resistance training, and you can, more or less, get the same benefits from most other forms of resistance training if you use good technique. Unfortunately most people are very sloppy about their technique, and do not get the full benefit From the effort they put into training.
Secondly, even people who intend on maintaining good form can let their technique slide over time without being aware of it. I believe this population will be very well served by training with kettlebells. The off-center weight distribution of the kettlebell will make it much easier to maintain good technique. However, you will still have to vigilant.
Thirdly, I've found that kettlebell training be very complimentary with my running. It helps to train muscular strength and endurance, joint mobility, balance, and body mechanics. All things that running does not do much to improve.
Some other points
It is very easy to create very well rounded training program using just kettlebells, but I would encourage everyone to add in other exercise modalities like body weight training, Olympic and power lifting, and plyometrics just to name a few. However, if you just have to pick one, kettlebell training would not be a bad choice.
There are two general styles of kettlebell lifting usually referred to as the "soft" style and the "hard" style. There does seem to be some rivalry between the two styles, but they both have a lot to offer. So keep an open mind, and look into them both. They are actually very complementary.