Putin is trying - at least - to grab Crimea, and currently has control of it. I'm thinking it's unlikely whatever Ukrainian government/forces remain after their recent revolution will wade into an all out war against the former USSR. Looks like Crimea just voted to join Russia, too. So I'd consider that one 'in the bag' for the Russians, unless somebody wants to get violent over the matter.
Bigger questions remain...
Will Russia try to branch out from beyond the traditionally Russian-leaning Crimean peninsula and go for the rest of Ukraine?
On what level - beyond press conferences and sanctions - will Western nations intervene?
Definitely many possible scenarios for very, very bad escalation of conflict here. Apparently, the Ukraine gave up their nukes in '94...but, doesn't take more than a little bit of bad book keeping to keep a few of those things around. Russia and EU countries have 'em, as does the U.S...bringing us back to the good ol' Cold War days.
What do you think will happen?