Most kettlebell exercises involve swinging the weight, with most of the work being done by the muscles around the hip.  Because the weight is offset from the handle this creates inertial forces which means the body has to work harder at stabilising the weight you are lifting.  The exercises, therefore, work your large muscles and core stabilising muscles simultaneously.

Swinging a kettlebell involves generating power to accelerate the weight, but it also involves absorbing balistic shock to decelerate the weight.  This is similar to plyometric training, and can aid power generation by the muscles

The exercises are incredibly metabolically demanding, which is why it is a great tool for burning fat.  But you will also develop strength, speed, power, coordination and flexibilty.

Anyone.  In recent years it has become the training tool of choice amongst celebrities, such as: Penelope Cruz, J-Lo and Madonna.  But they're not just for girls. The 300 actors trained with them to gain their Spartan warrior look, Tiger Woods uses them to improve his core strength for golf, and Lance Armstrong is a fan.  Kettlebells are used by the Russian military as their primary fitness tool.

Over the last 2 years I have trained many people from all walks of life with kettlebells.  All have seen fantastic results.  Training 1-to-1 will give you the greatest benefits, but I recognise that this is not affordable for many people.  As a result I now run group kettlebell classes at Hills Road Sixth Form College.  Email alan@bodytrain.co.uk to register your interest.  I also run group classes at Cambridge University Press, however, you need to be a member of staff to take part in these sessions.