We registered in two places for one shower. We registered at a big box store that was in town and another big box store for people from outlying areas that lived closer to the bigger cities that had both stores. We just made sure to register for the same things on both that we needed several of (bottles, sleepers, socks, etc.) and then tried to balance the bigger stuff (swing at one store, saucer at another).
Honestly, a registry is a guide for people that want to use it. It was great for groups that wanted to go together to get us a bigger, more expensive item to understand our taste but a lot of people just got what they found useful or what struck them as cute at the store. :) I really liked that one of the stores sent us a "completion" discount about a month before baby was born. It was like 20% items on our own registry which was a big help on the breast pump!