This is a great discussion guys. I am adding my 2 cents because I recently started going to my local Crossfit affiliate to supplement to my ultrarunning and climbing. The best way to train for any sport is to do it, of course, especially climbing since it involves good technique, not just 'generic' strength and endurance.
However, I find the variety and intensity of Crossfit exercises are improving my core strength, coordination and upper body strength, which in turn benefit my climbing.
I used to do regular gym workouts and was well self-motivated, but never trained with a personal trainer. The Crossfit method of group workouts under the eye of an instructor really appeals to me, to my surprise. Group ratios are usually small enough that it is akin to having a personal trainer giving expert advice. Not to mention pushing you to get 5 more box jumps before time is up
Crossfit also emphasizes the need for a healthy diet to complement and support the workouts - either the Zone Diet or the Paleo diet. They are worth looking into for those concerned with weight loss but personally I am having a hard time giving up ALL starchy carbs - I need my boiled potatoes with salt on long runs!!