If you are carrying 2 cameras with you and need a camera strap to allow you to carry both and easily switch from using one to the other then the BlackRapid DR-1 double strap may be the solution that you are looking for.

I recently purchased one of these and used it for about 6 hours during a wedding shoot and it worked great for me.

It comes with 2 tripod screws, one for each camera.  They are easy to install and are smooth and polished so that as you move the camera around it will move easily and not catch or snag.  It also has adjustable stops to limit how far the camera can move on the strap so as to limit free movement when you put the camera back down to your side.  The design makes it pretty comfortable to have two cameras on and ready for quick use.  I was shooting with a Canon 1D MKIII with a 70-200 2.8 lens and a Canon 60D with a 24-70 2.8 lens and did not feel too overloaded and the weight seemed pretty evenly distributed.  I am 6′ 3″ and found this to fit me quite comfortable and it was everything I had expected.  Another nice feature is that you can “dis-assemble” the straps to use each one independently if you are just using one camera.  For me it is a highly recommend!