Ignoring the fact it's a midterm year, 2014 is shaping up to be the GOP version of 2012. The polls were in the right direction, but actually underestimated their party's strength. They carried nearly every toss up. And they've even picked up a few races no one thought they would.
Per Nate Silver:
The pre-election polling averages in the 10 most competitive Senate races had a
6-percentage point Democratic bias as compared to the votes counted in each state so far.
http://fivethirtyeight.com/liveblog/special-coverage-the-2014-midterms/?#livepress-update-20407872The only thing we know about systematic polling failure: sometimes it will happen and it's impossible to predict which party will benefit from it.