A seeming UFO was captured by numerous sources moving slowly over the Olympic venue during the opening night fireworks display. Close analysis of the video shows that the object was functioning like a lighter than air craft, not like something that doesn’t need lift. Therefore your Out There editor comes down in favor of the idea that it was a blimp. No markings on it, though, I’ll give you that. 

Story Source:
http://www.youtube.com/watch?v=gtoZSiDZ58k