if you are doing DPS, you need to go 28 points madness (full creeping death), if not all 31.
I've heard some people do madness hybrid with 17 points in lightning for backlash like this:
but it's a DPS tradeoff for sure.
Generally speaking, the sorcerers who do bubble hybrid are heal/hybrids, because they can get away with using only 21-24 points in the corruption tree and all they really lose is the AOE heal which alone isn't going to save anyone's life. It's just an output score padder.