This will get ugly before it gets better because of the ethnic Russians in Ukraine. It will not turn out like Georgia did in 2008.
This demonstrates how different Russia views the world compared to everyone else, and the influence that they are able to have with those on their borders.
Budapest Memorandum doesn't mean jack, except for the petulant whining that is going on right now for Russia to stop it (memo was about nukes). Strongly worded statements are all that is going to be issued. Nobody wants to risk war with Russia, which means they will do as they please. I think the best that the Ukraine can hope for is a partitioned country where the Crimea becomes part of Russia.