Most of the seats up in 2014 are Dem seats, and many are vulnerable seats, such as Kay Hagan's.
The ACA debacle has turned what was looking like a likely win into a toss-up there. (and this is with a Dem base that is energized for next year due to the idiocy the Tea Partiers have done at the state level)
When it's election time next year, ACA website issues will all be forgotten and the many of the benefits of ACA will be in effect, I think that's going to make a big difference.