I know I've worried about a Russian invasion despite my conflicted feelings about what Russia should or would do, but events do seem to point to a window for Russia to invade in the next couple days.
Consider:
Ukrainian forces have been making gains in the east against the pro-Russian elements incited by Russian special forces and intelligence people, meaning that the Crimea scenario of a subliminal invasion is less likely to succeed.
Russia has a nice body count of pro-Russian elements in Odessa to justify their repeated claims that ethnic Russians are under attack.
Russia says it is passing along to a concerned Putin streams of calls from within Ukraine asking for Russia's help.
Russian troops are still prepared to strike and we are still within the window of opportunity based on Russia's intake of conscripts and discharge of more experienced soldiers completing their term of service.
Russia released those OSCE monitors held by pro-Russian elements in the east, clearing the decks so to speak, and eliminating any chance of their deaths under Russian control while Russian troops are on the move inside Ukraine.
Elements in the east of Ukraine who want to join Russia plan a referendum on May 11--and voting always goes better for Putin when his guys are in charge, on the ground.
So yeah, while I have worried about a Russian invasion before, I am again worried about an invasion over this weekend. Give the Russians a few days to road march through the eastern salient of Ukraine in the east and overcome token Ukrainian army resistance, and the Russians could have a triangle of territory that passes from Kharkov in the north south through Donetsk and on to the Sea of Azov.
With Crimea, I think that would be considered a good day's work for 2014, and Russia will seek to consolidate their territorial gains for now, and wait for further efforts to destabilize Ukraine to counter Kiev's move to the west and reopen divisions within Ukraine for further Russian inroads in the future.
In the meantime, Russia could shift their focus to central Asia and the former Soviet "stans" of that region to see what gains they can make in the meantime.