I'm guessing that Russia won't invade the Ukraine.
Putin is all about remaining in power and expanding Russia's influence. Should he invade Ukraine - probably a popular action amongst Russians - mass causalities will likely ensue. On top of that, economic sanctions from the West will result; in a few years, Putin's popularity might plummet and he could possibly lose power.
In all, an invasion is too risky. Meanwhile, amass troops on Ukraine's borders, and rattle the sabre - popular among Russians, relatively risk free - and who knows, maybe something in Putin's favor results.