they have their place.
I use them extensively with my bootcamps and group training. 1-2 kettlebells per person and I can train them for an hour with a full body, HIIT-style workout (including bodyweight stuff and cardio of course).
but, that's for "regular" people who just want to get into shape.
for bodybuilding?
I use them for delts when I do lateral raises. the weight of the kb forces your hands into the proper position.
I use them for overhead 1 arm extentions (triceps) because the handle is comfortable and the weight is balanced. plus, I can do them palm's-up, rather than 'heel of the palm up' as with a dumbbell.
I use them sometimes for curls, for the same reason I use them for lateral's... the weighted bottom forces your palm flat, and you don't need to 'squeeze' the handle, you can do the curls with an open palm/hand and avoid forearm fatigue. the range of motion with curls is limited though, due to the size of the kb and it hitting the forearm, so i'll do the curls leaning forward or with a concentration curl (standing, since the large kb's with hit the floor if done seated).
