It does add very minimal bulk, the Standard battery door almost fits with the new battery. However the "extended" battery is only 2100 mAh, and the standard battery is 1850 so it isn't gaining you very much, maybe an extra 30 mins of screen on time.
I use the extended battery but am not impressed, I wish they would have stretched the battery longer like they did on the Bionic and Razr so the extended battery wouldnt of added much thickness but provided much more mAh.