I dress mine the same occasionally.
I never set out to, but when I had my second daughter 22mths after my first, several people turned up at the hospital with matching outfits for them both which thrilled Megs, and I admit I thought they looked adorable. I wasn't done regularly, simply beacuse I had many hand-downs, but for family do's, parties, photo sittings etc I did. And when I had my third daughter.....
I sometimes do the same for my boys too, but not as often as they both suit different colours.
I have always planned to stop as each of them got older, as I assumed they would complain, but only esterday I took the eldest two girls out shopping with their birthday money, only for them both to buy the exact same outfit, right down to the same earings.......At least it proves to me that as much as they bicker at times, they obviously love being sisters and being the same.
I have even found tho, that when Megan goes out shopping with her best friend, they buy the same outfit too........Proof to me that girls love to be the same!