My L-plate from RSS just arrived, and it's sweet. All rounded, fits like a glove, couldn't be smaller, and it's easy to get to the batteries and ports.
What's more, the grip actually feels good in the had when held in portrait orientation (unlike the RSS L-plate for the gripped 5DII). My initial thought is that I just might not take it off. Indeed, with the Black Rapid attached to one of those little Wimberley clamps attached to the side (not bottom) of the clamp, the camera feels (almost) as good in the hand in portrait orientation as in landscape. Honestly, the worst part is that the center of gravity shifts to the outside (which, of course, is what the grip does all by itself). Other than that...well, again, it feels good. The L-plate is more of a continuation of the grip than something bolted on as an afterthought.
Yeah, the whole rig is big and bulky and heavy -- of course. But it's not at all uncomfortable.