A number of us training YSB in Beijing have added a bit of kettlebell training into our weekly routines. A special thanks must go to Johan for getting us started on kettlebells and also to Pavel Tsatsouline who really seems to be one of the best instructors out there; his technique looks clean and his explanations are well-thought (if you are looking for instructional information, check out Pavel's "Enter the Kettlebell").
The advantages of kettlebell training:
Kettlebells are appealing because they are highly transportable (they're like a mobile gym), give a great result (they are good for cardio and strength), they are fun (you can swing them over your head and throw them!) and they employ a large degree of coordinated full-body strength (which is similar to what YSB requires).
What weight is appropriate:
Kettlebell training originated in Russia so bells are generally measured in kilos (one kilo is roughly 2.2 pounds) so I will stick to that system here. Pavel suggests that men of average strength start out with a 16kilo bell, strong men with a 24 kilo and powerlifters only with a 32 kilo bell. This, of course, is not set in stone; in Beijing we started working with 2 20 kilo bells (which is plenty hard and it took a bit of time for me to get accustomed). It should also be noted that kettlebell training requires a lot of overhead strength, a factor to consider when choosing the weight of one's first bell. Also, two bell exercises are much harder to do with heavier bells than one bell exercises, so it depends on which exercises you prefer.
As you get stronger, you can increase the weight as needed; I mostly work with 24 & 32 kilo bells now for my single-handed training. Of course, if you mainly do double-handed exercises, you may have to work up the weight a bit slower.
Pavel's focus on press & pull: Pavel believes the two most important types of kettlebell exercises are presses and pulls. These can be broken into military presses & get ups (a static press) and swings & snatches (throws behind the back would also technically be a type of pull). Of the four exercises, the press is the least full-body (unless one cleans before reps), though it still gives great results. While the snatch is harder on the skin than the swing, it also seems to be the superior exercise of the two (one can almost always swing more than one can snatch). [Also note that snatches and cleans are done differently with kettlebells than standard weights. The snatch motion for kettlebells begins with more of a swing, which make the motion harder on the arm. The difference in the clean motion is even more significant, where one effectively spins the bell around one's arm; if one cleans the bell as one would a regular weight, the kettlebell will bash the forearm, defeating the point of the exercise).
If presses & pulls are the main exercises trained, one cannot go wrong; however, it should be noted that none of these (save perhaps the get up) does much to train the legs (though there is a lot of hip action with the pulls). Also, unless someone is trying something super rough such as a one-legged squat with a bell extended overhead, most exercises for the legs would be greatly assisted by a second bell.
Other exercises: There are a variety of other exercises that can be done from renegade rows (with a push up between each row, making the exercise much harder), to different types of squats, to thrusters (a squat with both hands pressing a bell overhead at the end) and so on. There are also a number of small movement exercises that can be done.
Circuits v. sets v. a singular set:
With kettlebells, there are also a variety of training methods that can be employed. Circuits are where one does a number of different exercises, non-stop, until the circuit is complete; one then does multiple circuits in this fashion. A circuit could have 3 - 8 different types of exercises and the number of exercises per circuit really depends on the number of reps one plans on doing per exercise (as well as the exercises themselves, their difficulty and the cumulative effects they produce on the body).
Sets are just when one does an amount of reps of one exercise, rests, and then repeats, perhaps doing 5-7 total sets. It is worth noting that kettlebell training generally requires many more reps per set than regular weight training. It simply takes more to wear things out because of the full-body motion and momentum generated by the bell.
A singular set is simply where one does a single set of a certain exercise and measures that set by time; for example, 10 minutes of snatching 24 kilos, trying to get as many reps as possible (upper 200's is preferable for that time...try one of these as your last exercise to cap off a strenuous workout; it'll kill you!).
Where to buy your kettlebell:
Buy American, not just because you are a wise patriot, but because the Chinese bells will literally rip the skin off your hands. I bought a Wisconsin-made bell from Lifeline USA and it blows every other bell I have seen out of the water. If you are buying a bell in Europe and don't want to go through the hassle/expense of importing an American bell, hopefully you can find a solid German, British or local manufacturor that makes high-quality kettlebells; but do your research, because a nice bell is simply a greater pleasure to train with. Lifeline's bells have a superior handle design & texture and have not once tore up my hands, even with snatch reps reaching 1000.
If you already have a Chinese-made kettlebell and are intent on making use of it, apart from avoiding excellent exercises that rub against the skin (e.g.: snatches), one could try to sand down the handle to see if that helps; but generally, desperate methods are probably not as welcome as paying a few extra bucks for a quality bell (when is the last time you needed to sand down a misshappen maglite or the door handle of your Ford?). You can also wear weightlifting gloves, but that will only slightly alleviate the stress a Chinese bell puts on the skin, perhaps enabling you to do an extra 20%.