I haven't decided yet whether I think Russia will invade eastern Ukraine. I have a horrible feeling Putin might settle for stirring up a civil war. There's obviously a small number of Russian special forces already in the east. They're there to coordinate the activities of the far larger number of pro-Russian thugs with Kalashnikovs, who may be good at beating up journalists and swaggering around with RPGs but are too dumb to be left in charge of intellectual things like tactics and strategy. The hope is that their provocations - or a violent Ukrainian government response - will incite locals to rebel against Kyiv.
Some commentators believe Putin will be content when he's achieved a federalised, Finlandised Ukraine. I have a nasty suspicion this won't be enough. Putin really wants to extinguish the memory of Euromaidan. He won't be happy until he has a puppet (Yanukovych or equivalent) back in charge on the Dniepr. He also needs to humiliate Ukraine, the largest of the ex-Soviet republics (apart from Russia, of course), and make an example of it to bring the others into line. A bloody civil war would achieve this.