Interesting...

(I actually put the "reduced NEO danger" bit in to stir things up a little, sorry. I realize that a change of 1 is hardly statistically significant).

Ol'khovatov makes several points that seem hard to reconcile with an impact event, and indeed most of the material I have read from other sources indicates a high degree of uncertainty about an asteroid/comet impact.

Some of his points:

1. Eyewitnesses give conflicting trajectories for the event, with at least three distinct paths being reported consistently.

2. Trees were blown down in a non-spherical pattern, and some of the blow-down was rotated. An air-burst would produce a perfectly spherical shock wave.

3. Trees show evidence of being burned after they were broken, that is, the heat arrived after the shock wave, which is inconsistent with a high-energy air burst.

4. Some trees near the supposed epicenter survived. With a 40 megaton air burst, everything near the epicenter should have been incinerated.

5. Seismic data is also inconsistent with an airburst, with effects being noted much further away than would be produced by an event at 8 km altitude.

6. No significant fragments or dust have been found, which is important even to the comet theory, as comets have a considerable solid component (probably chondritic-type material).

7. An unusualy sky-glow was noted in Siberia and many other areas for several days before the event. A comet tail would be too tenuous to produce such effects, especially if the comet were not visible prior to the exposion.

From what I've seen, the strongest arguement for a space-body impact seems to be... "what else could it have been?"