I just saved factor scores for a 2-dimensional IRT model in Mplus. But I would appreciate to get SE's (posterior SD's) too. Mplus can compute the information curve, so perhaps it wouldn't be too difficult to output score SE's too, as these can be computed from the information. (I assume the standard formula SE=1/sqrt(info) is valid in this case too.) Of course I could read the information from the Info curve, but not so exactly and it also takes some time to do.