A quick calculation.  Even at current levels (which include the absence of MKP-SMK, which is looking increasingly likely), a Smer-SNS coalition would have just barely enough to sustain a majority.  If Smer loses even 4 points from its current level (down to 34%) or Smer loses 3% and SDKU gains 1%, then Smer loses its ability to form a government with SNS.  The final result may not be as resounding a victory as the exit polls suggested, but it still bodes fairly well for the current opposition (except, maybe, MKP-SMK).