My DD (almost 3) and I did PSB and Cinderella's Gala Feast on our recent trip. She wore her dress to PSB but then changed not long afterwards - she wanted to play in the water jets and I explained it wouldn't be much fun with all that fabric hanging on her - or words to that effect.
I was able to stuff the dress and petticoat into her backpack that we took with us daily to hold extra clothes, snacks, etc. It stayed on her stroller and wasn't any problem to keep with us until we were ready to return to our room for a rest.
At PSB, I'd say that the ratio of girls in costume to those not was 1 in 3 or 1 in 4. I didn't see any girls not in costume who seemed really upset that they weren't. Here she is before we were seated:
She also wore a gown to Cinderella's Gala Feast - the one she has on in my sig. It seemed like there were more girls wearing princess costumes for that but that could be because it was the end of the day so the parents didn't have to worry about carrying a change of clothing.
My DD loved wearing hers but I made sure they did not itch. The bodices of both are lined with a soft cotton fabric and any seams that had netting in them were "encased" in the softer fabric. She did not complain when wearing either dress and probably would have worn them longer but I was concerned about the heat. She did not wear "princess shoes" though - just the sandals we'd brought for her to wear with any other oufit.
BTW - We saw a few girls each day who must have worn their dresses the whole day. Most had on very lighweight ones such as the Disney Stores sell.
