| There is a method which allows X and Y sperm to be separated to a reported 80% degree of success for X and I think a 70% for Y. The process involves, if I remember correctly, staining the nuclei of the sperm, and then a laser refractometer separates the sperm into 2 "gates" according to the amount of stain uptake. I think the method has been shown to work, at least better than random chance, but I've never read any scientific papers on it, so I'm not sure. The problems are: the sperm sample must be very large; the sperm are kind of "beaten up" by the whole process, so the necessary in vitro fertilization following segregation leads to smaller numbers of successful embryos; it's very expensive; there's only 1 place in the country (maybe in the world) where it can be done. The risks are that nobody really knows yet if the dye causes any subtle genetic damage after fertilization; and in vitro fertilization always has a higher risk of genetic defects, low birth weight babies, developmental delay, etc.
Amniocentesis can be used to detect Down's syndrome, and the parents can be given the option of abortion.
I'm also pretty sure that there already exists the technology whereby in vitro embryos can be screened for certain well known genetic defects. They harvest a cell from the embryo at a stage when it won't be "missed" (the 8 cell or 16 cell stage, I think, but I could be wrong). If the cell shows the obvious genetic marker for the disease, the embryo is discarded. I'm sure that with the human genome mapping having been completed, more and more genetic markers for disease will be discovered. As the demand for genetic screening increases (assuming it does), the techniques for embryo screening will no doubt improve.
Gene therapy using retroviruses to alter the DNA of grown individuals in order to correct genetic diseases is still in its infancy, but advancing quickly. Some successes have been seen with cystic fibrosis, I believe, but again I'm not sure. I know other attempts have been disappointing, but I can't remember what's been tried. There doesn't seem to be anything that would prevent the process from being theoretically possible, anyway.
All of the foregoing is just to point out that the future is already here. The technology will improve. I don't believe the genie will be placed back in the bottle. The only choice we will have is whether to utilize the technology for our children or not.
And yes, it is VERY scary. | 
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