Like Fraser said, "The discovery of dark energy was one of the biggest surprises in astronomy." But never the less, it must be considered carefully before any monumental change is made to mainstream thinking.

Immediately, right off the bat, the feeling is best described as uncomfortable that such a repulsive force could reside within the parameters of our known, visible, familiar expanding universe. It will take years of hard work to put the math to it that can be accepted as mainstream.

One simple answer that is against the mainstream is that our known, visible, familiar expanding universe is expanding into a greater universe of lower energy density. There is as big or bigger problem with that view because it might seem that the only clue to the existence of such a greater universe is the acceleration itself if you are strongly ensconced in the mainstream.

If science can put any comprehensible explanation and math together to keep it a repulsive force from within our familiar playing field they are committed to do that. IMHO, only as a last resort and with the greatest evaluation, study, theorizing and serious debate will science ever be able to say, "Maybe we are expanding into a greater universe." And that process is probably the way it should be but discussion of the possibilities is still an appropriate part of such a deliberate approach.