I couldn't do it. It's a great option for a lot of people and Seido makes great batteries, so if you want it, you can't go wrong.
One of my smart phone requirements is that I can fit it into the little pocket on the right front of my jeans, and unless I carry a blow torch and the jaws of life that won't happen with the big battery.
I also carry my sig P238 with a nylon in the pants holster which is on the same side, the clip for it is just behind that pocket The epic touch works out better then my evo, as the evo was effectively twice the thickness. I did try a friends out on my evo and it was worse then carrying my 7 inch tablet (without case) in my front pocket.