I was actually going to start a thread asking all the people who had doubts about the USO theme whether they were now willing to eat crow, but now I have this convenient thread in which I can apparently say the same thing a lot of other people are saying.
t:
It's true, I remember how many people were worried once we heard about the USO scene. People were afraid of seeing Cap "singing and dancing". Most ominously, they thought that by putting Cap in the original Kirby costume, in a ridiculous context - as Joe Johnston said, where Cap would "himself feel like an idiot when he wore it" - the director was basically saying how little respect he had for the source material.
I think we can all agree that what eventually showed up on screen was a very pleasant surprise. To me, it actually strengthened the portrayal of Steve Rogers' character. People have asked why he ended up doing it, but to be fair, his commanding officers basically gave him two choices in the movie - as Peggy stated, to be a "lab rat or a dancing monkey". If anything, it strengthened one of the core themes of the movie - Steve's desire to serve his country but being prevented from doing so, or at least in the way he imagined. The movie begins with him wanting to join the war effort, but not being able to do so due to his weak physical condition. The USO element extends this: even after he gets buffed out from the Super Soldier Serum, Steve is still prevented from joining his countrymen on the front lines. Despite his miraculous transformation, he still hasn't got what he wanted; he's still separated from all the ordinary Joes fighting the war effort. In my opinion, it makes his eventual decision to go AWOL behind enemy lines to save Bucky that much more powerful.
Beyond that, the montage was funny, entertaining and touched on the historical purpose of the Captain America character - as a propaganda creation and a symbol of America's fighting spirit. And let's not forget that terrifically catchy Alan Menken song, which surely makes it all worthwhile.