[icegreentea]

Well, the point of science is that we don't know until we observe it. So it shouldn't be that astounding since we've had a ridiculously hard time getting large amounts of neutral antimatter (everything before was charged, so EM affects overwhelmed gravitational). The consensus seems to be that antimatter will behave 'normally'. but we haven't seen it yet. Also, it turns out that certain frameworks where anti-matter is repelled by matter gravity doesn't violate anything else that hasn't already been violated (for example, CP and CPT symmetry have already be observed to be broken). And thus the uncertainty.

[Jach]

Hold on, where are you getting the CPT-symmetry violation from? This paper http://arxiv.org/abs/0801.0287v4 has a collection of experimental results hinting at that but the conclusion does not as yet seem to be very strong.