Speaking as a complete novice on all matters Russian and Eastern European, I find the events in Ukraine very troubling indeed. It looks to me very much as though Putin is embarked on an effort to reconstitute as much of the Soviet Union as he can. It is clearly not in our national interest to launch a war to stop him, and there seems not to be any other forced that could pose an obstacle to the effort. Will he move on Belarus? Does he have his eye on Kazakhstan, Turkmenistan, Uzbekistan, and Kyrgyzstan? I think it very unlikely he will make a move against Lithuania, Latvia, and Estonia.
The United States has an airbase in Kyrgyzstan which must close in July of this year, and the Air Force is talking about moving it to Kazakhstan, at least for as long as it is needed to support military operations in Afghanistan. I would guess Putin will be patient enough to wait until we pull out of Central Asia.
Russia's imperial expansion has always been limited to areas contiguous with its central territory, in much the same way as that of China, making it extremely difficult to challenge geopolitically. [Contrast that with the imperial expansions of France, Great Britain, Germany, Holland, Spain, Italy, and the United States, or with ancient Rome and Athens, for that matter.]
I suspect economic sanctions, which could be quite costly for Russia, will have not the slightest impact on any imperial aspirations Putin may have.
This is serious business, folks, but despite the inevitable tough talk from neo-cons and attacks on Obama as a gutless wimp, my guess is that no one is actually going to make a serious effort to take America into a ground war with Russia. There is very little for us to do save wait and see how it plays out in Eastern Europe.