I think dressing a yorkie is personal preference, not a good or bad thing. I personally dress Couver in sweaters and jackets when its cold, or a t-shirt when it's chilly. But now that the weather is nicer, the only thing he wears is a bow!
I think it's cute, but I don't go overboard. It's not his favorite thing to do so I try to limit when he has to wear clothes.