Obama has announced that he will not pursue Bush's plan for expanding land-based missile defense systems to Eastern Europe. I am sure that the right wing will argue that Obama is selling out the East Europeans, as this has been a major thorn in the side of Russia-US relations. There is more to it than that, including how expensive the program is (not to mention of somewhat dubious reliability). Ricks suggests that this decision is a boon for the US Navy, which can station ships in the Black Sea (regularly or during a crisis?) to shoot down Iranian missiles.
Obama did notify the concerned countries ahead of time, and their reactions seemed to be mixed, with Poles perhaps quite annoyed. Poland has been one of the largest contributors of troops to NATO's effort in Afghanistan and has been a steadfast supporter of the US. This will not change, as Poland obviously sees NATO's raison d'etre to be still relevant--the Russian threat.
UPDATE: Fred Kaplan sees this as good news too