Can mean that the writer is confused, raising an eyebrow, and/or shocked but not about to say it. See o.O
"I'm a monkey! Roar I say, ROAR!!"
We don't really know, but if you use it, you're a "cool" internet user, like me.
"nubz0r 1: leik omg wuttup
nubz0r 2: nmu
nubz0r 1: be neither lawl
nubz0r 2: o.0"