See the paper http://arxiv.org/abs/1103.4937 by M. Villata for an argument for antimatter falling up. However, see D.J. Cross at http://arxiv.org/abs/1108.5117 for powerful rebuttal arguments, asserting that Villata misapplied the CPT theorem, resulting in an incorrect sign for the matter-antimatter gravitational interaction.
See http://lss.fnal.gov/archive/test-fn/0000/fermilab-fn-0822-cd-t.pdf for a general review of the previously existing experimental evidence from Etvos and other experiments such as accelerometers, Kaons, astrophysical neutrino's from SN1987A.