Black Rapid deservedly has a lot of very happy users, and for good reason, it's an evolved design and they just work
. I also use the quite amazing Spider Pro System http://www.spiderholster.com/
This gets the bodies off the neck & shoulder, and puts the weight on the hips. It's a great setup for events shooting and sports like track & field where I routinely shoot with 3 bodies, two of which travel on the Spider Pro belt. They are 1-Series bodies with 24-70 and another with 70-200. A 300 f/2.8 is on a third body on a monopod. I can RUN with this setup.
But this is still an evolving science. Just a little heads up about the attachment method of both Black Rapid and the Spider Pro pins. They screw into either the tripod thread on the base of the body, or into the thread in the collar of longer lenses like 70-200 and 300 f/2.8 etc. Was this designed to handle the stresses imposed by a body and weighty lens? The thread in the lenses will be fine, but the thread on the base of bodies may not be up to the job. Think about how this thread is attached into the body. It's not tapped into the body proper, it's an insert into the body.
Some time ago when threading a Spider Pro pin into the grip of a 5D body, the thread insert just popped straight out of the grip. Admittedly I was tightening it pretty firmly, but still...makes you think dunnit?