Satellite integration

Something else I've also wondered - Some years back, I was at a payload processing convention for the VentureStar (yes, I can admit it, I was a true geek) and while there, someone was seemed to imply that integration between a satellite and standard rockets was fairly standardize, with a common berthing mechanism between the rocket and the satelitte. Basically, what I am wondering is, how hard is it to swap a satellite out of a rocket, both in the design phase, construction phase, and basically all the way up until launch.