My 2 cents please?
*Perhaps this should be in the politics forum*
Just my opinion of course (or my theory based on past observations)...
Neither Russia or the United States will use large nuclear weapons against each other. Depleted Uranium shells and bullets maybe, but not full ICBM nukes.
Both countries, as in both countries military leaders and political leaders know the seriousness of embarking on that path. It didn't happen when the US were assisting to defend Iraq in the eighties, and I doubt it will happen in Georgia.
Having said that, I also believe that US pseudo-involvement in this current war between Georgia and Russia is because of the previously mentioned oil pipelines. Whoever controls those pipelines controls a major part of the worlds oil supplies.
I find it interesting after having done some quick reading, that Georgia appears to have started this by attacking Ossetia. Now I am more convinced that the US political involvement is oil based. For example, there are wars and conflicts occurring in Africa that the US is ignoring, even though some of these wars are more genocide than war. The reason for not intervening? Where is the oil? Remember the Bosnian war? No-one got involved even though thousands of innocents were dying. No economic advantage in defending either side.
Last but not least, even if Russia and the US did go to war, it wouldn't be WW3 until their respective allies became actively involved and also declared war on the opposing side.
I was just trying to think of a name for a war between Russia and the US and I thought about Terminator...wasn't that big war that the movie is based around an oil war originally? Oh no, that was the skynet robots going troppo...