I feel a bit bad about laughing at this
1st fail: the sound is horrible in Dancing Queen, a lot of them kept falling out and the light is all over the place. Taeyeons mic seems to be completely broken.
2nd fail: You can hear the difference between the playback and their voices on I got a Boy, making it very obvious that some of them can't really sing that well under pressure. Like Sunny can't too high, Yoona is very nasal, Sooyoung has a bad start, Fanys voice is a lot darker live, Hyoyeon can't keep up with her own rap. Taeyeon seems to be the only one without playback, OR her mic is so broken that we can only hear the playback. Seo and Jessica impressed me here, voices very close to the "CD".
Poor girls :/