If you followed oral arguments, this is not much of a surprise. And, it was the right decision - it wasn't a decision "for" gay marriage or "against" gay marriage, but rather a decision on the more important question of "who decides?".
Not only was the court right on the merits, I sense they knew that a ruling striking down Prop 8 would certify California as a banana republic. And it would have. No doubt we will see a political initiative attempting to reverse Prop 8 - precisely as it should be.
This issue remains a tempest in a teacup - I can think of 25 other issues that deserve priority over this political battle, and I am being charitable with that number. But, it is interesting that New York and now California - both liberal vanguards among states in the Union - recognize that the issue is a political one.