Anyone use them?

I do not know a PT who does not these days.

They are a useful tool in the right circumstances. There are a number of applications for cricket.

http://www.harrowdrive.com/want-to-know-a-secret-of-cricket-power/

tried them- wot a let down. So much hype.

what the blazes is a kettle ball? 

They are simply an alternative way to add resistance to training. If you listen to the hype you would feel let down, but as a tool they are effective at what they do.

true say. But people go on about them like they an amazing new thing that will revolutionsie training- like they will give u something that nothing else can and that you dont need to use anything else- i suppose its just modern marketing.

Courtesy of hp from the Rotator cuff Clinic thread:

http://uk.youtube.com/watch?v=RqyIuFIdgRk

As you can see from the background, they increase in weight like dumbbells.  The problem is, people are not too sure how to use them 

The reason PTs would use a kettlebell over a dumbbell in this exercise is for safety.  They are a lot more versatile.  The larger, heavier ones are great for sled training