Oh, you really want a phylo discussion on this.
Er, no, actually, we don't. The Politics and Religion Forum is the place for a philosophical discussion of the ethics of gender selection.
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I don't see how "Is it safe?" could refer to pre-fertilization sperm sorting, so I have not addressed it. I'm assuming you're talking about embryo biopsy.
I presume when you're asking, "Is it safe?" you mean, "Is it safe for the embryo to have cells removed from it?"
Here are two sites that discuss the procedure.
http://www.religioustolerance.org/abo_pgd.htm
http://www.emedicine.com/med/topic3520.htm
The E-Medicine article refers to only 700 surviving (successfully born) children who have had this done so far, and the procedure itself is comparatively new. Thus, I would assume that it's really too soon to tell whether it's harmful to a human being to have one or two cells removed from it while it's still in the 8-cell blastocyst stage.
As for whether the OP's link's quoted 99.9% success rate for embryo biopsy can be true--I don't see why not. Many of the genetic disorders embryo biopsy is being used to screen for are sex-linked disorders, like hemophilia, so they must be able to tell, and it seems like kind of a no-brainer to simply check whether the cell in question has X or Y chromosomes.
Bear in mind that this procedure is not cheap, but if you're already spending the bucks for IVF, I suppose you wouldn't stick at spending a bit more to at least get the desired gender. "In for a penny, in for a pound", etc.