slappy sam wrote in post #2598421
My first question is whether or not you think canon plans to release a successor that will be better or cheaper (and equivalent) to the 580EX anytime in the next few months.
My second question is when you use the battery grip on the rebel, do you not load batteries into the main compartment? Because if you did then you wouldn't double your battery life with the grip, you'd triple it.
Can't answer your first question because my grandson dropped my crystal ball so it's not working anymore. 
But re your 2nd question, the way the battery grip works is, there's a part on it that actually goes into the battery compartment to connect with contacts in there (that's how the power from the batteries in the grip gets to the camera. So, no, you can't have batteries in the camera battery compartment if you are using the battery grip. 