Originally Posted by
Andrey 
But why YouTube is gone?
Same reason Google Maps are no longer preloaded. I agree; Apple's YouTube implementation was darn good, but there's a Google-made app out now (iPhone only).
You can also go to YouTube.com. Going forward, all I can see in that future is ads, which makes me less likely to ever use YouTube again at all once I get an iOS 6+ device.
Until then, I'll enjoy my ad-free iOS 5 YouTube app, I guess. And ad-free YouTube on the desktop.