I'm coming late to this party but I promised myself that I would always share my story when the collar question comes up. My 5 dogs have breakaway collars to hold their tags when we take them out of the house or there is a tornado watch in effect. In the house they do not wear anything and here is why:
http://www.yorkietalk.com/forums/general-yorkshire-terrier-discussion/155756-thank-god-cpr.html
I remember that Magansmomma had all three of hers run out an open gate and got them back within minutes because they were wearing their tags so there are two trains of thought. I understand her feelings about always having the collars on and she certainly understands my opposite feelings.