I suspect you'd still need 'supports' added when slicing - as often it's not so much gravity, but movement from the print head that causes things to go awry.
As for layer/bed adhesion. Even here on Earth, the RepRap MendelMax/Lulzbot [1] can print upside down. I imagine that's true for most of the units made from aluminum extrusions. And there have already been prints done in parabolic 'zero-g' flights using a Makerbot looking printer [2].
