From what I've seen reported, several people have assumed that the meteor that streaked across Siberia and exploded was actually a pair of meteors in close formation, which is why there were two smoke trails.
It's a pretty wild idea that the meteor could have been a stable lifting body shape, on top of the mere fact of the meteor itself! Even wilder and more fantastic (in the literal sense), seeing as how the double trail continues after the knot-like portion of the cloud, is the possibility that the meteor maintained a stable lifting shape through an incredibly huge explosion.
Perhaps it looked like one of our early experiments on the shapes that eventually led to the Space Shuttle:
Or perhaps there was some other dynamic at work. But, going by the shape of the smoke trail, I bet there was lift and stability involved.
In this video, you can see the gigantic lingering fireball from the explosions:
Somewhat relatedly, if you have any moronic friends who go on about "chemtrails," send them to Contrail Science.
Update 10 AM Feb. 17, 2013: Location corrected from Siberia to Chelyabinsk
Update 10 PM Mar. 5, 2013: Reflecting on this post, I now believe that I had the whole phenomenon upside down. In the video, you can clearly see the fireball rising, as of course any hot pocket of air would (in this case an incredibly large and toasty "pocket"). That's effectively that 757 picture turned upside down. The line of hot rising smokey air would split to either side into the parallel vortices that you see. In that case, the meteor would be a non-lifting disintegrating/exploding body of material, per the typical characterization of a meteor. It's like a nuclear bomb's mushroom cloud, in linear form. Perhaps what threw me off was the clear gap between the smoke vortices.